AU2010201358B2 - Communication protocol system and method for a distributed-architecture heating, ventilation and air conditioning network - Google Patents

Abstract

COMMUNICATION PROTOCOL SYSTEM AND METHOD FOR A DISTRIBUTED-ARCHITECTURE HEATING, VENTILATION AND AIR CONDITIONING NETWORK 5 The disclosure provides an HVAC data processing and communication network (200) and a method of manufacturing the same. In an embodiment, the network includes a system device (290) and a subnet controller (230a). The system device is adapted to provide a service and publish a 10 message including a device status vector representing an availability of the system device to provide the service. The subnet controller is adapted to receive the message from the system device including the device status vector via a data bus (180). 2625173-1 148 HVAC SYSTEM - -110 AIR COMFORT 1 6 0 HANDLER(S) SENSOR(S) 120 CONTROLL 150 I ~ FURNACE(S) UNIT(S 130 EVAPORATOR I DISPLAY(S) 170 146 DEMAND UNIT r - - - - - - -- - - - - ,155 I CONDENSER I DAMPER (ZONE 1142 COILS) CONTROLLER) 115 140 ' COMPRESSOR(S) 144 L---------------------- J HVAC DATA PROCESSING AND COMMUNICATION NETWORK 215 -N DAMPER j COMFORT 260 CONTROLLER(S) SENSOR(S) r 210, AIR HANDLER ACTIVE SUBNET 230a CONTROLLER(S) CONTROLLER(S) 220 INTEGRATED FURNACE USER INTERFACE/ 250 CONTROLLER(S) GATEWAY (Ul/G) INACTIVE SUBNET 180 USER 230i CONTROLLER(S) INTERFACE 240 UNITARY LOCAL 225 CONTROLLER CONTROLLER - 290

Description

S&F Ref: 946947 AUSTRALIA PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT Name and Address Lennox Industries Inc., of 2100 Lake Park Boulevard, of Applicant: Richardson, Texas, 75080, United States of America Actual Inventor(s): Wojciech Grohman Address for Service: Spruson & Ferguson St Martins Tower Level 35 31 Market Street Sydney NSW 2000 (CCN 3710000177) Invention Title: Communication protocol system and method for a distributed-architecture heating, ventilation and air conditioning network The following statement is a full description of this invention, including the best method of performing it known to me/us: 5845c(2628271_1) - 1 COMMUNICATION PROTOCOL SYSTEM AND METHOD FOR A DISTRIBUTED-ARCHITECTURE HEATING, VENTILATION AND AIR CONDITIONING NETWORK CROSS-REFERENCE TO RELATED APPLICATIONS 5 This application claims the benefit of U.S. Provisional Application Serial No. 61/167,135, filed by Grohman, et al., on April 6, 2009, entitled "Comprehensive HVAC Control System", and is a continuation-in-part application of Application No. 10 12/258,659, filed by Grohman on October 27, 2008, entitled "Apparatus and Method for Controlling an Environmental Conditioning Unit," both of which are commonly assigned with this application and incorporated herein by reference. This application is also related to 15 the following U.S. patent applications, which are filed on even date herewith, commonly assigned with this application and incorporated herein by reference: Serial No. Inventors Title 12/603,464 Grohman, "Alarm and Diagnostics System et al. and Method for a Distributed Architecture Heating, Ventilation and Air Conditioning Network" 12/603,534 Wallaert, "Flush Wall Mount Control Unit et al. and In-Set Mounting Plate for a Heating, Ventilation and Air Conditioning System" 12/603,449 Thorson, "System and Method of Use for a et al. User Interface Dashboard of a Heating, Ventilation and Air Conditioning Network" 12/603,382 Grohman "Device Abstraction System and Method for a Distributed Architecture Heating, Ventilation and Air Conditioning Network" 12/603,526 Grohman, "Communication Protocol System et al. and Method for a Distributed Architecture Heating, Ventilation and Air Conditioning Network" 'C1 7 ' I - 2 12/603,527 Hadzidedic "Memory Recovery Scheme and Data Structure in a Heating, Ventilation and Air Conditioning Network" Grohman "System Recovery in a Heating, Ventilation and Air Conditioning Network" 12/603,473 Grohman, "System and Method for Zoning a et al. Distributed-Architecture Heating, Ventilation and Air Conditioning Network" 12/603,525 Grohman, "Method of Controlling et al. Equipment in a Heating, Ventilation and Air Conditioning Network" 12/603,512 Grohman, "Programming and Configuration et al. in a Heating, Ventilation and Air Conditioning Network" 12/603,431 Mirza, et "General Control Techniques in al. a Heating, Ventilation and Air _Conditioning Network" TECHNICAL FIELD This application is directed, in general, to HVAC networks and, more specifically, to systems and methods 5 for logical manipulation of system features. BACKGROUND Climate control systems, also referred to as HVAC systems (the two terms will be used herein interchangeably), are employed to regulate the 10 temperature, humidity and air quality of premises, such as a residence, office, store, warehouse, vehicle, trailer, or commercial or entertainment venue. The most basic climate control systems either move air (typically by means of an air handler having a fan or blower), heat 15 air (typically by means of a furnace) or cool air (typically by means of a compressor-driven refrigerant loop). A thermostat is typically included in a conventional climate control system to provide some level of automatic temperature and humidity control. In its 20 simplest form, a thermostat turns the climate control ') r P,1 '7' -1 - 3 system on or off as a function of a detected temperature. In a more complex form, the thermostat may take other factors, such as humidity or time, into consideration. Still, however, the operation of a thermostat remains turning the climate control system on or off in an attempt to maintain the temperature of the premises as close as possible to a desired set point temperature. Climate control systems as described above have been in wide use since the middle of the twentieth century and have, to date, generally provided adequate temperature management. SUMMARY One aspect provides an HVAC data processing and communication network. In an embodiment, the network includes a first system device and a subnet controller. The first system device is adapted to provide a first service and publish a message including a first device status vector representing an availability of the first system device to provide the first service. The subnet controller is adapted to receive the message from the first system device including the first device status vector via a data bus. The subnet controller is further adapted to receive, via messages from a plurality of system devices including the first system device, a corresponding plurality of device status vectors that includes the first device status vector, where each device status vector includes a plurality of bits, each bit having within the device status vector a bit position that corresponds to one of a plurality of potential services provided by the system devices, where the plurality of services including the first service. Another aspect is a method of manufacturing a HVAC data processing and communication network. In an embodiment, the method includes configuring a first system device and a subnet controller. The first system device is configured to provide a first service and publish a message including a first device status vector representing an availability of the first system device to provide the first service. The subnet controller is configured to receive the message from the first system device including the first device status vector via a data bus. The subnet controller is further configured to receive, via messages from a plurality of system devices including said first system device, a corresponding plurality of device status vectors that includes said first device status vector, wherein each device status vector includes a plurality of bits, each bit having within said device status vector a bit position that corresponds to one of a plurality of potential services provided by said system devices, said plurality of services including said first service Yet another aspect is a system device for use in an HVAC data processing and communication network. In an embodiment, the system device includes a physical layer interface, a demand unit and a local controller. The physical layer interface is adapted to couple the system device to a data bus. The demand unit is configured to provide an HVAC service. The local controller adapted to publish a message including a device status vector representing an availability of the demand unit to provide the HVAC service. BRIEF DESCRIPTION Reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which: - 4a FIG. 1 is a high-level block diagram of an HVAC system according to various embodiments of the disclosure; FIG. 2 is an embodiment of the disclosure of a network layer associated with the HVAC system; FIG. 3 is a block diagram of a local controller of the disclosure; FIG. 4 is a block diagram of a system device of the disclosure; FIG. 5 illustrates an example grouping of devices on an RSBus subnet; FIG. 6A is an embodiment of an HVAC data processing and communication network having two subnets; FIG. 6B illustrates an embodiment of selectively isolating subnets; FIG. 7 illustrates field definitions of an example message frame of the disclosure; FIG. 8 illustrates an error frame of the disclosure; FIG. 9 illustrates an embodiment of a Class 1 message format of the disclosure; - 5 FIG. 10A illustrates an embodiment of a Class 3 device status message format of the disclosure; FIG. 10B illustrates an embodiment of a Class 3 alarm message format of the disclosure; 5 FIG. 11 illustrates an embodiment of a Class 5 subnet controller message format of the disclosure; FIG. 12 is a method of the disclosure illustrating startup of a local controller; FIGs. 13A and 13B are methods of the disclosure 10 illustrating startup of a subnet controller; FIG. 13C is a state table an example state machine implementing a method of starting up a subnet controller; FIG. 14 is a method of the disclosure illustrating an algorithm that may be employed by a subnet controller 15 to assign Equipment Type to a device; FIG. 15 is a method of the disclosure of conducting a dialog between a subnet controller and a demand unit according to the disclosure; and FIGs. 16-24 illustrate various methods of the 20 disclosure. DETAILED DESCRIPTION As stated above, conventional climate control systems have been in wide use since the middle of the twentieth century and have, to date, generally provided 25 adequate temperature management. However, it has been realized that more sophisticated control and data acquisition and processing techniques may be developed and employed to improve the installation, operation and maintenance of climate control systems. 30 Described herein are various embodiments of an improved climate control, or HVAC, system in which at least multiple components thereof communicate with one another via a data bus. The communication allows - 6 identity, capability, status and operational data to be shared among the components. In some embodiments, the communication also allows commands to be given. As a result, the climate control system may be more flexible 5 in terms of the number of different premises in which it may be installed, may be easier for an installer to install and configure, may be easier for a user to operate, may provide superior temperature and/or relative humidity (RH) control, may be more energy efficient, may 10 be easier to diagnose, may require fewer, simpler repairs and may have a longer service life. FIG. 1 is a high-level block diagram of a networked HVAC system, generally designated 100. The HVAC system 100 may be referred to herein simply as "system 100" for 15 brevity. In one embodiment, the system 100 is configured to provide ventilation and therefore includes one or more air handlers 110. In an alternative embodiment, the ventilation includes one or more dampers 115 to control air flow through air ducts (not shown.) Such control may 20 be used in various embodiments in which the system 100 is a zoned system. In an alternative embodiment, the system 100 is configured to provide heating and therefore includes one or more furnaces 120, typically associated with the one or more air handlers 110. In an alternative 25 embodiment, the system 100 is configured to provide cooling and therefore includes one or more refrigerant evaporator coils 130, typically associated with the one or more air handlers 110. Such embodiment of the system 100 also includes one or more compressors 140 and 30 associated condenser coils 142, which are typically associated with one or more so-called "outdoor units" 144. The one or more compressors 140 and associated condenser coils 142 are typically connected to an -7 associated evaporator coil 130 by a refrigerant line 146. In an alternative embodiment, the system 100 is configured to provide ventilation, heating and cooling, in which case the one or more air handlers 110, furnaces 5 120 and evaporator coils 130 are associated with one or more "indoor units" 148, e.g., basement or attic units that may also include an air handler. For convenience in the following discussion, a demand unit 155 is representative of the various units 10 exemplified by the air handler 110, furnace 120, and compressor 140, and more generally includes an HVAC component that provides a service in response to control by the control unit 150. The service may be, e.g., heating, cooling, humidification, dehumidification, or 15 air circulation. A demand unit 155 may provide more than one service, and if so, one service may be a primary service, and another service may be an ancillary service. For example, for a heating unit that also circulates air, the primary service may be heating, and the ancillary 20 service may be air circulation (e.g. by a blower). The demand unit 155 may have a maximum service capacity associated therewith. For example, the furnace 120 may have a maximum heat output (often expressed in terms of British Thermal Units (BTU) or Joules), or a 25 blower may have a maximum airflow capacity (often expressed in terms of cubic feet per minute (CFM) or cubic meters per minute (CMM)) . In some cases, the demand unit 155 may be configured to provide a primary or ancillary service in staged portions. For example, a 30 blower may have two or more motor speeds, with a CFM value associated with each motor speed. One or more control units 150 control one or more of the one or more air handlers 110, the one or more n - 11'7j '1 1 - 8 furnaces 120 and/or the one or more compressors 140 to regulate the temperature of the premises, at least approximately. In various embodiments to be described, the one or more displays 170 provide additional functions 5 such as operational, diagnostic and status message display and an attractive, visual interface that allows an installer, user or repairman to perform actions with respect to the system 100 more intuitively. Herein, the term "operator" will be used to refer collectively to any 10 of the installer, the user and the repairman unless clarity is served by greater specificity. One or more separate comfort sensors 160 may be associated with the one or more control units 150 and may also optionally be associated with one or more displays 15 170. The one or more comfort sensors 160 provide environmental data, e.g. temperature and/or humidity, to the one or more control units 150. An individual comfort sensor 160 may be physically located within a same enclosure or housing as the control unit 150, in a manner 20 analogous with a conventional HVAC thermostat. In such cases, the commonly housed comfort sensor 160 may be addressed independently. However, the one or more comfort sensors 160 may be located separately and physically remote from the one or more control units 150. Also, an 25 individual control unit 150 may be physically located within a same enclosure or housing as a display 170, again analogously with a conventional HVAC thermostat. In such embodiments, the commonly housed control unit 150 and display 170 may each be addressed independently. 30 However, one or more of the displays 170 may be located within the system 100 separately from and/or physically remote to the control units 150. The one or more displays '?) r 111 - 9 170 may include a screen such as a liquid crystal or OLED display (not shown). Although not shown in FIG. 1, the HVAC system 100 may include one or more heat pumps in lieu of or in 5 addition to the one or more furnaces 120, and one or more compressors 140. One or more humidifiers or dehumidifiers may be employed to increase or decrease humidity. One or more dampers may be used to modulate air flow through ducts (not shown). Air cleaners and lights may be used to 10 reduce air pollution. Air quality sensors may be used to determine overall air quality. Finally, a data bus 180, which in the illustrated embodiment is a serial bus, couples the one or more air handlers 110, the one or more furnaces 120, the one or 15 more evaporator condenser coils 142 and compressors 140, the one or more control units 150, the one or more remote comfort sensors 160 and the one or more displays 170 such that data may be communicated therebetween or thereamong. As will be understood, the data bus 180 may be 20 advantageously employed to convey one or more alarm messages or one or more diagnostic messages. All or some parts of the data bus 180 may be implemented as a wired or wireless network. The data bus 180 in some embodiments is implemented 25 using the Bosch CAN (Controller Area Network) specification, revision 2, and may be synonymously referred to herein as a residential serial bus (RSBus) 180. The data bus 180 provides communication between or among the aforementioned elements of the network 200. It 30 should be understood that the use of the term "residential" is nonlimiting; the network 200 may be employed in any premises whatsoever, fixed or mobile. Other embodiments of the data bus 180 are also - 10 contemplated, including e.g., a wireless bus, as mentioned previously, and 2-, 3- or 4-wire networks, including IEEE-1394 (Firewirem", i.LINKm, LynxT m ), Ethernet, Universal Serial Bus (e.g., USB 1.x, 2.x, 3.x), 5 or similar standards. In wireless embodiments, the data bus 180 may be implemented, e.g., using Bluetoothm, Zibgee or a similar wireless standard. FIG. 2 is a high-level block diagram of one embodiment of an HVAC data processing and communication 10 network 200 that may be employed in the HVAC system 100 of FIG. 1. One or more air handler controllers (AHCs) 210 may be associated with the one or more air handlers 110 of FIG. 1. One or more integrated furnace controllers (IFCs) 220 may be associated with the one or more 15 furnaces 120. One or more damper controller modules 215, also referred to herein as a zone controller module 215, may be associated with the one or more dampers 115. One or more unitary controllers 225 may be associated with one or more evaporator coils 130 and one or more 20 condenser coils 142 and compressors 140 of FIG. 1. The network 200 includes an active subnet controller (aSC) 230a and an inactive subnet controller (iSC) 230i. The aSC 230a may act as a network controller of the system 100. The aSC 230a is responsible for configuring and 25 monitoring the system 100 and for implementation of heating, cooling, humidification, dehumidification, air quality, ventilation or any other functional algorithms therein. Two or more aSCs 230a may also be employed to divide the network 200 into subnetworks, or subnets, 30 simplifying network configuration, communication and control. Each subnet typically contains one indoor unit, one outdoor unit, a number of different accessories including humidifier, dehumidifier, electronic air ncncl -71) 1 - 11 cleaner, filter, etc., and a number of comfort sensors, subnet controllers and user interfaces. The iSC 230i is a subnet controller that does not actively control the network 200. In some embodiments, the iSC 230i listens to 5 all messages broadcast over the data bus 180, and updates its internal memory to match that of the aSC 230a. In this manner, the iSC 230i may backup parameters stored by the aSC 230a, and may be used as an active subnet controller if the aSC 230a malfunctions. Typically there 10 is only one aSC 230a in a subnet, but there may be multiple iSCs therein, or no iSC at all. Herein, where the distinction between an active or a passive SC is not germane the subnet controller is referred to generally as an SC 230. 15 A user interface (UI) 240 provides a means by which an operator may communicate with the remainder of the network 200. In an alternative embodiment, a user interface/gateway (UI/G) 250 provides a means by which a remote operator or remote equipment may communicate with 20 the remainder of the network 200. Such a remote operator or equipment is referred to generally as a remote entity. A comfort sensor interface 260, referred to herein interchangeably as a comfort sensor (CS) 260, may provide an interface between the data bus 180 and each of the one 25 or more comfort sensors 160. The comfort sensor 260 may provide the aSC 230a with current information about environmental conditions inside of the conditioned space, such as temperature, humidity and air quality. For ease of description, any of the networked 30 components of the HVAC system 100, e.g., the air handler 110, the damper 115, the furnace 120, the outdoor unit 144, the control unit 150, the comfort sensor 160, the display 170, may be described in the following discussion - 12 as having a local controller 290. The local controller 290 may be configured to provide a physical interface to the data bus 180 and to provide various functionality related to network communication. The SC 230 may be 5 regarded as a special case of the local controller 290, in which the SC 230 has additional functionality enabling it to control operation of the various networked components, to manage aspects of communication among the networked components, or to arbitrate conflicting 10 requests for network services among these components. While the local controller 290 is illustrated as a stand alone networked entity in FIG. 2, it is typically physically associated with one of the networked components illustrated in FIG. 1. 15 FIG. 3 illustrates a high-level block diagram of the local controller 290. The local controller 290 includes a physical layer interface (PLI) 310, a non-volatile memory (NVM) 320, a RAM 330, a communication module 340 and a functional block 350 that may be specific to the demand 20 unit 155, e.g., with which the local controller 290 is associated. The PLI 310 provides an interface between a data network, e.g., the data bus 180, and the remaining components of the local controller 290. The communication module 340 is configured to broadcast and receive 25 messages over the data network via the PLI 310. The functional block 350 may include one or more of various components, including without limitation a microprocessor, a state machine, volatile and nonvolatile memory, a power transistor, a monochrome or color 30 display, a touch panel, a button, a keypad and a backup battery. The local controller 290 may be associated with a demand unit 155, and may provide control thereof via the functional block 350, e.g. The NVM 320 provides local - 13 persistent storage of certain data, such as various configuration parameters, as described further below. The RAM 330 may provide local storage of values that do not need to be retained when the local controller 290 is 5 disconnected from power, such as results from calculations performed by control algorithms. Use of the RAM 330 advantageously reduces use of the NVM cells that may degrade with write cycles. In some embodiments, the data bus 180 is implemented 10 over a 4-wire cable, in which the individual conductors are assigned as follows: R - the "hot" - a voltage source, 24 VAC, e.g. C - the "common" -a return to the voltage source. 15 i+ - RSBus High connection. i- - RSBus Low connection. The disclosure recognizes that various innovative system management solutions are needed to implement a flexible, distributed-architecture HVAC system, such as 20 the system 100. More specifically, cooperative operation of devices in the system 100, such as the air handler 110, outdoor unit 144, or UI 240 is improved by various embodiments presented herein. More specifically still, embodiments are presented of communications protocols 25 among networked HVAC devices that provide a robust means of communicating within an installation site, and simplified configuration of the system relative to conventional systems. FIG. 4 illustrates a device 410 according to the 30 disclosure. The following description pertains to the HVAC data processing and communication network 200 that is made up of a number of system devices 410 operating cooperatively to provide HVAC functions. Herein after O)C')C 11 1 - 14 the system device 410 is referred to more briefly as the device 410 without any loss of generality. The term "device" applies to any component of the system 100 that is configured to communicate with other components of the 5 system 100 over a wired or wireless network. Thus, the device 410 may be, e.g., the air handler 110 in combination with its AHC 210, or the furnace 120 in combination with its IFC 220. This discussion may refer to a generic device 410 or to a device 410 with a 10 specific recited function as appropriate. An appropriate signaling protocol may be used to govern communication of one device with another device. While the function of various devices 410 in the network 200 may differ, each device 410 shares a common architecture for interfacing 15 with other devices, e.g. the local controller 290 appropriately configured for the HVAC component 420 with which the local controller 290 is associated. The microprocessor or state machine in the functional block 350 may operate to perform any task for which the device 20 410 is responsible, including, without limitation, sending and responding to messages via the data bus 180, controlling a motor or actuator, or performing calculations. A system status display 430 is described below. 25 In various embodiments, signaling between devices 410 relies on messages. Messages are data strings that convey information from one device 410 to another device 410. The purpose of various substrings or bits in the messages may vary depending on the context of the 30 message. Generally, specifics regarding message protocols are beyond the scope of the present description. However, aspects of messages and messaging nrncl~ I - 15 are described when needed to provide context for the various embodiments described herein. FIG. 5 illustrates an embodiment of the disclosure of a network of the disclosure generally designated 500. 5 The network 500 includes an aSC 510, a user interface 520, a comfort sensor 530 and a furnace 540 configured to communicate over a data bus 550. In some embodiments these devices form a minimum HVAC network. In addition, the network 500 is illustrated as including an outdoor 10 unit 560, an outdoor sensor 570, and a gateway 580. The furnace 540 and outdoor unit 560 are provided by way of example only and not limited to any particular demand units. The aSC 510 is configured to control the furnace 540 and the outdoor unit 560 using, e.g., command 15 messages sent via the data bus 550. The aSC 510 receives environmental data, e.g. temperature and/or humidity, from the comfort sensor 530, the furnace 540, the outdoor sensor 570 and the outdoor unit 560. The data may be transmitted over the data bus 550 by way of messages 20 formatted for this purpose. The user interface 520 may include a display and input means to communicate information to, and accept input from, an operator of the network 500. The display and input means may be, e.g., a touch-sensitive display screen, though embodiments of the 25 disclosure are not limited to any particular method of display and input. The aSC 510, comfort sensor 530 and user interface 520 may optionally be physically located within a control unit 590. The control unit 590 provides a convenient 30 terminal to the operator to effect operator control of the system 100. In this sense, the control unit is similar to the thermostat used in conventional HVAC systems. However, the control unit 590 may only include 1) __)r_1 -7 ) 11 - 16 the user interface 520, with the aSC 510 and comfort sensor 530 remotely located from the control unit 590. As described previously, the aSC 510 may control HVAC functionality, store configurations, and assign 5 addresses during system auto configuration. The user interface 520 provides a communication interface to provide information to and receive commands from a user. The comfort sensor 530 may measure one or more environmental attributes that affect user comfort, e.g., 10 ambient temperature, RH and pressure. The three logical devices 510, 520, 530 each send and receive messages over the data bus 550 to other devices attached thereto, and have their own addresses on the network 500. In many cases, this design feature facilitates future system 15 expansion and allows for seamless addition of multiple sensors or user interfaces on the same subnet. The aSC 510 may be upgraded, e.g., via a firmware revision. The aSC 510 may also be configured to release control of the network 500 and effectively switch off should another SC 20 present on the data bus 550 request it. Configuring the control unit 590 as logical blocks advantageously provides flexibility in the configuration of the network 500. System control functions provided by a subnet controller may be placed in any desired device, 25 in this example the control unit 590. The location of these functions therein need not affect other aspects of the network 500. This abstraction provides for seamless upgrades to the network 500 and ensures a high degree of backward compatibility of the system devices 410 present 30 in the network. The approach provides for centralized control of the system, without sacrificing flexibility or incurring large system upgrade costs. ')C C 1 '7 ) 1 - 17 For example, the use of the logical aSC 510 provides a flexible means of including control units on a same network in a same conditioned space. The system, e.g., the system 100, may be easily expanded. The system 5 retains backward compatibility, meaning the network 500 may be updated with a completely new type of equipment without the need to reconfigure the system, other than substituting a new control unit 590, e.g. Moreover, the functions provided by the subnet controller may be 10 logically placed in any physical device, not just the control unit 590. Thus, the manufacturer has greater flexibility in selecting devices, e.g., control units or UIs, from various suppliers. In various embodiments, each individual subnet, 15 e.g., the network 500, is configured to be wired as a star network, with all connections to the local controller 290 tied at the furnace 120 or the air handler 110. Thus, each indoor unit, e.g., the furnace 120, may include three separate connectors configured to accept a 20 connection to the data bus 180. Two connectors may be 4 pin connectors: one 4-pin connector may be dedicated for connecting to an outdoor unit, and one may be used to connect to equipment other than the outdoor unit. The third connector may be a 2-pin connector configured to 25 connect the subnet of which the indoor unit is a member to other subnets via the i+/i- signals. As described previously, a 24 VAC transformer associated with the furnace 120 or air handler 110 may provide power to the system devices 410 within the local subnet via, e.g., the 30 R and C lines. The C line may be locally grounded. FIG. 6A illustrates a detailed connection diagram of components of a network 600A according to one embodiment of the disclosure. The network 600A includes a zone 605 - 18 and a zone 610. The zones 605, 610 are illustrated without limitation as being configured as subnets 615, 620, respectively. The subnet 615 includes an air conditioning (AC) unit 630, a UI/G 640, an outdoor sensor 5 (OS) 650, a control unit 660, and a furnace 670. The control unit 660 includes an SC 662, a UI 664 and a comfort sensor 666, each of which is independently addressable via a data bus 180a. The subnet 620 includes a control unit 680, a heat pump 690 and a furnace 695. 10 The control unit 680 houses an SC 682, a UI 684 and a comfort sensor 686, each of which is independently addressable via a data bus 180b. In various embodiments and in the illustrated embodiment each individual subnet, e.g., the subnets 615, 620 are each configured to be 15 wired as a star network, with connections to all devices therein made at a furnace or air handler associated with that subnet. Thus, e.g., each of the devices 630, 640, 650, 660 is connected to the data bus 180a at the furnace 670. Similarly, each device 680, 690 is connected to the 20 subnet 620 at the furnace 695. Each furnace 670, 695, generally representative of the indoor unit 148, may include a connection block configured to accept a connection to the RSBus 180. For example, two terminals of the connection block may be 4-pin connectors. In one 25 embodiment, one 4-pin connector is dedicated to connecting to an outdoor unit, for example the connection from the furnace 670 to the AC unit 630. Another 4-pin connector is used to connect to equipment other than the outdoor unit, e.g., from the furnace 670 to the UI/G 640, 30 the OS 650, and the control unit 660. A third connector may be a 2-pin connector configured to connect one subnet to another subnet. In the network 600A, e.g., the subnet 615 is connected to the subnet 620 via a wire pair 698 ')C ) r-1 "7 1 - 19 that carries the i+/i- signals of the serial bus. As described previously with respect to the furnace 120, a transformer located at the furnace 670 may provide power to the various components of the subnet 615, and a 5 transformer located at the furnace 695 may provide power to the various components of the subnet 620 via R and C lines. As illustrated, the C line may be locally grounded. This approach differs from conventional practice, in 10 which sometimes a master controller has the ability to see or send commands to multiple controllers in a single location, e.g., a house. Instead, in embodiments of which FIG. 6A is representative there is no master controller. Any controller (e.g. the SCs 662, 682) may communicate 15 with any device, including other controllers, to make changes, read data, etc. Thus, e.g., a user located on a first floor of a residence zoned by floor may monitor and control the state of a zone conditioning a second floor of the residence without having to travel to the 20 thermostat located on the second floor. This provides a significant convenience to the user, who may be a resident, installer or technician. FIG. 7 illustrates an example embodiment of a message frame generally designated 700. The message frame 25 700 is configurable to send messages between one local controller 290 and another local controller 290, e.g., between the UI 240 and the AHC 210. It is to be understood that the message frame 700 is but one of several possible schemes to communicate between local 30 controllers 290. Those of skill in the pertinent arts will recognize that other equivalent schemes are within the scope of the disclosure. n -- ) I7' - 20 Messages may be communicated in a manner compatible with a two-wire bus architecture. In some cases, a controller-area network is an appropriate communication standard. In an example embodiment, messages follow a 5 format based on the Bosch CAN2.OB (hereinafter "CAN") standard. The following aspects of the CAN standard are described by way of example, with no implied limitation on messaging formats otherwise within the scope of the disclosure. 10 As will be appreciated by those skilled in the pertinent art, the bus in the CAN standard can have one of two complementary logical values: "dominant" or "recessive". During simultaneous transmission of dominant and recessive bits, the resulting bus value will be 15 dominant. For example, in case of a wired-AND implementation of the bus, the dominant level would be represented by a logical 0 and the recessive level by a logical 1. In this context a dominant bit is a bit that "wins" when a dominant and a recessive bit are 20 simultaneously asserted on the CAN bus. As illustrated in FIG. 7, a single message frame may include a Start of Frame (SOF) bit 710, an Arbitration Field (AF) 720, a Control Field (CF) 730, a Data Field (DF) 740, a CRC Field 750, an ACK Field 760 and an End of 25 Frame (EOF) Field 770. Each message frame starts with a dominant SOF bit 710, e.g., a logical 0. At least some of the local controllers 290 on the network 200 that are ready to transmit messages synchronize to the SOF bit 710 30 generated by the local controller 290 that initializes the transmission. In some cases, the SC 230 performs the initialization. This aspect is discussed in greater detail below. It may be preferable in some cases that all - 21 of the local controllers 290 on the network 200 synchronize in this manner. The AF 720 may include a number of bits as identifier (ID) bits. The illustrated embodiment includes 5 two subfields. A first subfield 722 includes, e.g., 11 base ID bits, while a second subfield 724 includes, e.g., 18 extended ID bits. This configuration is an example of a CAN extended format. Those skilled in the pertinent art will appreciate that in other embodiments, a standard 10 format message frame 700 may be used. An SRR bit and an IDE bit separate the first subfield 722 and the second subfield 724, and a RTR bit ends the AF 720. In some embodiments the SRR bit and IDE bit are always set to 1 and the RTR bit is always set to 0. 15 In the message frame 700 the CF 730 is illustrated as including, e.g., two reserved bits RO and Rl and a 4 bit Data Length Code (DLC) Field. The reserve bits are always sent as recessive, but the receivers should accept them without any errors regardless if they are recessive 20 or dominant. The DLC Field determines the number of bytes in the DF 740. The DF 740 may range from 0 to 64 bits. The case of 0 bits, of course, represents the special case that no data is send by the message frame 700. In all but this 25 special case, data may be segmented into multiples of 8 bits (bytes) with maximum of 8 bytes. The CRC Field 750 contains a checksum calculated on the SOF bit 710, the AF 720, CF 730 and DF 740. The CRC field 750 is illustrated in this example embodiment of 30 the CAN standard as being 15 bits wide. Of course other CRC widths may be used where appropriate for other communication standards. The computation of the CRC may be determined as per the CAN2.0 standard, e.g. The CRC 9?9r,) 1 '7 -- 1 - 22 field 750 is terminated in a suitable manner, e.g., by a Delimiter Bit that is always recessive. The ACK field 760 is two bits long and contains an ACK SLOT (ACK) and an ACK delimiter (Del). A transmitting 5 local controller 290, e.g., the SC 230, sends two recessive bits. A receiving local controller 290, e.g., the AHC 210, reports the correct receipt of a message to the transmitting local controller 290 by asserting a dominant bit during the ACK slot. Thus the transmitting 10 local controller 290 can detect that another local controller 290 is present on the network to receive the message. However, the acknowledgement by the receiving local controller 290 does not confirm the validity of the message data. 15 The EOF field 770 is delimited by a flag sequence of seven consecutive recessive bits. The CAN standard prohibits the occurrence of more than five consecutive bits of a same value in the SOF bit 710, the AF 720, the CF 730, the DF 740, and the CRC 20 field 750. Whenever a transmitting local controller 290 detects five consecutive bits of identical value in the bit stream to be transmitted it automatically inserts a complementary bit in the actual transmitted bit stream. The CAN standard defines five types of errors that 25 are not mutually exclusive: Bit Error - while sending any bits on the bus, the transmitting local controller 290 also monitors the bus. When the state of the bus is detected to be different from the intended state, a bit error normally occurs. 30 Exceptions to this general case include when a recessive bit is sent in an AF 720 and a dominant bit is read back. This event signifies a case of lost arbitration rather than a bit error. The ACK field 760 is sent as a )C')1 7~ 1 - 23 recessive bit. When at least one other active local controller 290 is present on the bus, in routine operation the local controller 290 sets the field to the dominant state. Note that a local controller 290 sending 5 a Passive Error Flag and detecting a dominant bit does not interpret this as a Bit Error. A bit error may indicate in some circumstances a collision between a message the local controller 290 is attempting to publish to the data bus 180 and a message published to the data 10 bus 180 by another local controller. Bit Stuffing Error: this error occurs when a 6th consecutive equal bit level is detected in the message field comprising the SOF bit 710, the AF 720, the CF 730, the DF 740 and the CRC field 750. 15 CRC Error: each receiving local controller 290 calculates the CRC in the same manner as the transmitting local controller 290. The CRC error is generated when the calculated value is different from the value received on the RSBus 180. 20 Form Error: this error occurs when a fixed-form bit field (a delimiter, EOF Field or inter-frame space) contains one or more illegal bits. For the receiving local controller 290, a dominant bit received in the EOF bit should not be considered an error. 25 Acknowledgment Error: this error represents the condition that the transmitting local controller 290 determines that no receiving local controller 290 has asserted a dominant bit during the ACK transmission as described above. 30 FIG. 8 illustrates an embodiment of an error frame, generally designated 800. The RSBus 180 may provide active and passive error frames in conformity with the CAN standard. The error frame 800 includes an error flag n7n)~ I - 24 field 810 and an error delimiter 820. The error flag field 810 may be superimposed. In an active error frame, the superposed flags are dominant, whereas in a passive error frame, the flags are recessive. 5 The majority of transmission errors may be addressed by retransmitting the message according to the CAN2.0 standard. More specifically, each error type listed above may be handled as follows: Bit Error: An Error Frame may be generated which 10 starts with the next bit-time. Bit Stuffing Error: A node that detects a violation of bit stuffing (e.g., more than 5 bits of the same state) may generate an Error Frame, which causes the sending local controller 290 to resend the message. 15 CRC Error: CRC may be calculated by both the receiving local controller 290 and the sending local controller 290. The sending local controller 290 includes the CRC in the message. If the CRC of the receiving local controller 290 fails to match the CRC in the message then 20 an error frame is generated. The sending local controller 290 may resend the message in response to the error frame. Form Error: A sending local controller 290 that detects a dominant bit in the Delimiter, End of Frame 25 (EOF) field or Inter-frame Space may generate an Active Error Frame. The sending local controller 290 may resend the message in response to the Active Error Frame. Acknowledge Error: At least one receiving local controller 290 is expected to set the acknowledge bit to 30 dominant after the message is sent by the transmitting local controller 290. If the acknowledge bit is not set to dominant, the sending local controller 290 may resend the message. 11 )E 7~ -3 1 - 25 Under certain conditions, a local controller 290 may be placed in a fault confinement condition to limit the operation thereof. Each local controller 290 keeps a count of detected transmit and receive errors. Under some 5 conditions, the local controller 290 may enter one of three error states: error active, error passive, and bus off. A local controller 290 is normally in the error active state. In this state the local controller 290 can 10 interrupt a current message in progress by signaling an error via an active error frame 800. The transmitting local controller 290 detects the active error frame 800 and resends the message as described above. Each local controller 290 may keep a separate count of transmit 15 errors and receive errors. The local controller 290 remains in the error active state until an error count exceeds a lower limit value. The limit value 127 may be chosen for convenience, but any desired number may be used. In some embodiments, the error value is 2"-1, n 20 being an integer. A local controller 290 enters the error passive state when either the transmit or receive error count exceeds 127. In the event that one of the error counts exceeds 127, the local controller 290 may generate an 25 alarm condition alerting the SC 230 to the error state. An alarm condition may be signified by a DEVICE Communications Problem alarm. The alarm may be cleared when the local controller 290 enters the error active state. In the error passive state, a local controller 290 30 is configured to refrain from interrupting a message in progress. The local controller 290 may, however, generate passive error frames 800. OlzDrl1'721 - 26 The local controller 290 enters the bus off state when the transmit error count exceeds an upper limit value. In some embodiments, the upper limit value is 2

"+

1, where n is the integer selected for the lower limit 5 value described above. Thus, in one example, if the lower limit value is 127, the upper limit value may be 255. When the error count exceeds the upper limit value, the affected local controller 290 is configured to refrain from sending messages on the RSBus 180. However, 10 the local controller 290 may continue to monitor activity on the RSBus 180. A local controller 290 which is in bus off state may enter the error active state after a reset. The device reset condition may be the expiration of a timer that starts upon the local controller 290 entering 15 the bus-off state. In an example embodiment, the timer expires after 5 minutes. When the local controller 290 is reset by any means, the local controller 290 may reset its transmit error count. Referring back to FIG. 7, each message frame 700 may 20 be limited in the amount of data that may be sent thereby. When implemented using the CAN2.0 standard, for example, the DF 740 can contain a maximum of eight bytes. In some cases, it may be desirable to send more than eight bytes of data from one local controller 290 to 25 another local controller 290. In such cases, the sending local controller 290 may send a message longer than eight bytes by partitioning the message into multiple message frames 700. A mechanism referred to as "transport protocol" is provided by some embodiments to enable 30 sending such messages. In some embodiments, this mechanism is based on the ISO/DIS Standard 15765-2, incorporated herein by reference as if reproduced in its entirety. Herein after, this standard is referred to as - 27 the "15765-2 standard" for brevity. The 15765-2 standard provides for message sequences that include up to 4095 bytes. The 15765-2 standard uses the addressing format as 5 described below with respect to the message addressing scheme. Thus transport protocol messages may follow the same format as other messages broadcast over the RSBus 180. However, transport protocol messages may be distinguished from non-transport protocol messages at the 10 appropriate layer of the protocol stack based on the ID of the message in question. Referring to FIG. 7, the DF 740 may include from 0 to eight bytes of data, where each byte comprises 8 bits. In some cases, a local controller 290 may need to convey 15 more than eight bytes of data to another local controller 290. In various embodiments the local controllers 290 are configured to implement full-duplex transport protocol communication. Such communication is defined, e.g., in 20 Section 6.7.3 of the 15765-2 standard. All local controllers 290, except the SC 230 and the UI/G 250, are single session transfer protocol devices. The SC 230 and the UI/G 250 support up to 4 concurrent transport protocol sessions. When single session devices are 25 engaged in a transport protocol receive session, they are not required to respond to a new transport protocol receive session request. In such cases the SC 230 and the UI/G 250 may ignore incoming first frames. The transmitting local controller 30 290 may then retry sending the first frame a number of times. In some embodiments, the requesting local controller 290 retries twice, each time after a one second timeout. If three consecutive attempts fail, the ') r C 1 '7 q-1 - 28 local controller 290 may issue an alarm signifying that the receiving local controller 290 is unresponsive and may abort the communication attempt. Analogously, the same single-session transport protocol device will not 5 request another transport protocol send session unless the currently ongoing send session is completed. In some embodiments, all single frame transport protocol messages are sent and received regardless of the state of the multi-frame send or receive sessions. 10 In some embodiments, a transport protocol block size is eight, and a separation time may be 5 ms. However, the local controllers 290 may be configured to use other values, or to override default values, when necessary for effective communication. 15 In some cases, one or more errors may be encountered during a transfer protocol session. Various embodiments provide error handling consistent with those described by the 15765-2 standard. Each logical local controller 290 on the RSBus 180 20 may be identified by an Equipment Type (ET) number. The Equipment Type number serves as an identifier of a class of logical local controllers 290. In some cases, there may be multiple Equipment Type numbers for a same device class. Table I below lists an example embodiment of 25 Equipment Type numbers for various classes of equipment. The values presented in Table I apply to this example embodiment, and are provided without limitation for illustration purposes. Those skilled in the pertinent art will recognize that various equivalents may be 30 implemented within the scope of the disclosure. Table I: RSBus Equipment Types Equipment Number Equipment Type Number Comments Type Range (in binary form) ) C )1"7 1 - 29 00 1- I'D un M' '1 N C4 .I- 4) 4~j 40 4-) 4-3 I 41 J) Active Subnet Oh - Fh 0 0 0 0 0 x x x x Subnet Controllers Controll er = Oh Furnace 10h 0 0 0 0 1 0 0 0 0 Air Handler llh 0 0 0 0 1 0 0 0 1 Air 12h 0 0 0 0 1 0 0 1 0 Heat Pump 13h 0 0 0 0 1 0 0 1 1 Humidifier 14h 0 0 0 0 1 0 1 0 0 Dehumidifie 15h 0 0 0 0 1 0 1 0 1 r Damper 16h Control 17h 0 0 0 0 1 0 1 1 X Modules ERV 18h 0 0 0 0 1 1 0 0 0 HRV 19h 0 0 0 0 1 1 0 0 1 Dual Fuel lAh 0 0 0 0 1 1 0 1 0 Module UV Light 1Bh 0 0 0 0 1 1 0 1 1 Media Air 1Ch 0 0 0 0 1 1 1 0 0 CleanerIII Electronic 1Dh 0 0 0 0 1 1 1 0 1 Air Cleaner IAQ lEh 0 0 0 0 1 1 1 1 0 Analyzer Winning lFh 0 0 0 0 1 1 1 1 1 Module Wireless Gateways may be conf igur ed at 20h or at 30h. Individu al Wireless 20h _ sensors Comfort 3Fh 0 0 0 1 x x x x x may then Sensors be added from that address on until a maximum number is reached, - 30 e.g., 32. Comfort 40h - 0 1 0 0 Sensors 4Fh A Wireless Gateway may be configur ed at 50h. Individu al Wireless addresse Outdoor 50h 0 0 1 0 1 x x x x s are Sensor 5Fh added to this base address to a maximum number of sensors, e.g., 16. The number of sensors Outdoor 60h 0 0 1 1 0 0 0 x on each Sensors 63h subnet may be limited, e.g., to 4. Not Used 64h 0 0 1 1 0 ? ? ? ? Expansio 6Fh n User Interfac User es are 70h - 70h Interfaces/ 7Fh 0 0 1 1 1 x x x x 7Bh. Gateways 7h7h Gateways are 7Ch - 7Fh Not Used 80h -1 ? ? ? ? ? ? ? ? Expansio lDFh n 1E~h -Reserved Reserved 1FF 1 1 1 1 x x x x x for NVM I__ I__ I I L ' I I ,Flashing In various embodiments, a local controller 290 may be configured to notify the aSC 230a that it cannot be configured as commanded. The notification may take the - 31 form of an appropriately configured message sequence from the local controller 290 to the aSC 230a. Table II below illustrates an embodiment of a message addressing scheme of the disclosure. A message ID 5 of this embodiment includes 29 bits, providing a pool of more than 5E8 different messages. This message pool is divided into eight message classes identified by the three most significant bits of the Message ID, bits 26 28. Each message class may be designated for a different 10 purpose, as indicate. In the illustrated embodiment, classes 0, 2, 4 and 7 are not currently defined. Table II: RSBus Message Classes CAN extended 29-bit message ID Message Class o C 1 o o H 0 o 1 o 0 . . e o H C o Class 0 0 0 0 Class 1 $ Destination or UI/G 0 0 1 co -- No Ln -m n a O' Source Equipment messages H H H Q Type H H H 0Ty E EE EHH H H QH C o H 1i -iH -- iH 1iH H H H H H EnU)U) ) Class 2 0 1 0 Class 3 Q4 a4 U Source Equipment Broadcast 0 11 Source1Equipmen N H oD Type messages H 4 aN oo r-- o m (N i-i c H H H H H H H H H H H H H -~m m mmmm mm mU1 U) U) U___ U~S. C U _ U_ iiU U) M Class 4 1 0 0 Class 5 E- Destination or SC 1 0 1 c Source Equipment messages H H H H H H H H H H H H H Type Ln in inin Ln in n Ln Ln Ln Ln Ln nU) U) U) Class 6 M CO i-, n ,; mn (N ri c) Diagnostic 1 1 0 o r N o o m C - C H H H H H H0 0 U) U) messages o co - o in o m (N oc- H H H H00 0a 0 0 0 10 H !class 7 111 1 1 1 1 1 - 32 In various embodiments, all message IDs on the RSBus 180 follow the described encoding, with one exception. For a transfer protocol flow control frame, the message ID may duplicate the message ID of the frame of the 5 received transfer protocol First Frame. The various message classes of Table II are now described. Message Class 1 includes User Interface and Gateway messages, e.g., those sent by the UI/G 250. These messages serve to communicate with the user during normal 10 system operation. They include messages sent from the user interface or the gateway, as well as some messages explicitly and implicitly addressed to them. FIG. 9 illustrates an embodiment of the disclosure of the AF 720 (FIG. 7) for Class 1 messages. The control 15 bits in the AF 720 are encoded as follows: Table III: Class 1 Message Arbitration Field Breakdown Sub-Field Description Purpose DSIO-DSI1 Destination Subnet Indicate the subnet Identifier the message is sent to SSIO-SSIl Source Subnet Indicate the subnet Identifier the message originated in UIIDO-UIID3 User Interface ID Indicate the address of the UI or G the message is sent to or from, values 0-11 denote User Interfaces, values 12-15 identify Gateways; it is equivalent to the UI/Gs Equipment Type numbers, offset by 70h - e.g. if the UI has the ET = 72h, its UIID = 2 Equipment Type Equipment Type Number As defined in Table I ClMIDO = ID17/TP Class 1 Message ID Least significant bit LSb/Transfer Protocol of the Class 1 Message ID. This bit indicates if the - 33 message is a Transfer Protocol message (TP = 1) or not (TP = 0) C1MIDO - ClMID8 = ID17- Class 1 Message ID Unique 9-bit message ID25 identifier within Class 1 FIG. 10A illustrates an embodiment of the disclosure of the AF 720 (FIG. 7) for Class 3, System Broadcast messages. System Broadcast Messages are broadcasted from one subnet, such as the subnet 400, but all local 5 controllers 290 from all subnets can listen and respond to a Class 3 message. System Broadcast messages include DEVICEStatus and Alarms messages. There are 8,192 (213) System Broadcast messages possible in the illustrated embodiment. The number of alarms is limited to a subset 10 of the total possible number of message, e.g. 1024 (210). The control bits in the AF 720 are encoded as follows for this message class: Table IV: Class 3 Message Arbitration Field Breakdown: System Broadcast Messages Sub-Field Description Purpose SSIO-SSI1 Source Subnet Indicate the subnet Identifier the message originated from AL Alarms AL = 0 indicates that the message is a system broadcast message. AL = 1 indicates an alarm AS All subnets AS = 0 indicates that the message is broadcast on all subnets. AS = 1 indicates that the destination subnet is identical to the source subnet Equipment Type Equipment Type Number As defined in Table I C3MIDO - C3MID12 = ID12- Class 3 Message ID Unique 13-bit message ID24 identifier within Class 3 15 - 34 FIG. 10B illustrates an embodiment of Class 3 messages for the case that the message is an Alarm message. In various embodiments, all Alarm messages are Class 3 messages. An Alarm message includes additional 5 information about the alarm priority encoded in the PRO PR1 bits. The control fields in the AF 720 are encoded as indicated in Table V. Table V: Class 3 Message Arbitration Field Breakdown: Alarm Messages Sub-Field Description Purpose SSIO-SSIl Source Subnet Indicate the Identifier subnet the message originated from AL Alarms Set to 1 to indicate an alarm PRO-PR1 Alarm Priority Encodes alarm priority, e.g., minor, moderate and critical SC Set/Clear Set to 0 when the alarm is set and set to 1 when the alarm is being cleared ID12-ID21 Alarm Number The exact representation of the alarm number AS All Subnets AS = 0 indicates that the message is broadcast on all subnets. AS = 1 indicates that the destination subnet is identical to the source subnet Equipment Type Equipment Type As defined in - 35 Number Table I FIG. 11 illustrates an embodiment of the disclosure of the AF 720 for Class 5, Subnet Controller messages. Messages in this class may be used primarily when a local controller 290 is in a COMMISSION state or a 5 CONFIGURATION mode. In some embodiments, all messages in class 5 are used for communication to or from the Subnet Controller, e.g., the SC 230. The format of messages in Class 5 may be constrained to be as defined in Table II. In FIG. 10B, ID14-ID25 identify a unique message 10 resulting in total of 4096 (212) messages in this class. Table VI describes the bit assignments in the AF 720 for Class 5 messages. The Equipment Type and the Destination Subnet Identifier denote the specific device and the specific 15 HVAC system (network subnet) to which the message is addressed when sent from the SC 230. If the message is sent to the SC 230, the Equipment Type identifies the device sending the message and the SSI bits identify the subnet of the device. The SC 230 being addressed is 20 identified by the Destination Subnet Identifier bits. During normal operation, a Subnet Identifier in device messages would typically not change unless the particular local controller 290 to which the device messages pertain is reconfigured to work on a different 25 subnet. The Equipment Type designator assigned to a local controller 290 typically does not change, but may be reassigned if the local controller 290 is reconfigured. Generally, local controllers 290 other than Subnet Controllers respond only to class 5 messages containing 30 their Equipment Type and Subnet ID in the destination field. 1r )r1 7 ) 1 - 36 Table VI: Class 5 Message Arbitration Field Breakdown: Subnet Controller Messages Sub-Field Description Purpose DSIO-DSIl Destination Indicate the Subnet Identifier subnet the message is sent to SSIO-SSIl Source Subnet indicate the Identifier subnet the message originated in Equipment Type Equipment Type As defined in Number Table I ClMIDO = ID13/TP Class 5 Message Least ID LSb/Transfer significant bit Protocol of the Class 5 Message ID. If 1, indicates the message is a Transfer Protocol message C5MIDO - C5MID12 = Class 5 Message Unique 13-bit ID13-ID25 ID message identifier within Class 5 Diagnostic messages are categorized as Class 6 messages. Class 6 messages use Device Designator bits to 5 identify the destination device. Even when the local controller 290 is not configured, or is disabled as described below, the local controller 290 can still send or receive Class 6 messages. In various embodiments, the local controller 290 can send and receive Class 6 10 messages before being configured or while disabled. The control bits in the AF 720 are encoded as described in Table II, and further detailed in Table VII. Table VII: Class 6 Basic Diagnostic Messages Sub-Field Description Purpose UIIDO-UIID3 User Interface Indicate the ID address of the UI/G the message - 37 is sent to or from. Values 0-11 may denote User Interfaces; values 12-15 may identify Gateways. The User Interface ID is equivalent to the UI/G Equipment Type numbers, offset by 70h. E.g., if the Equipment Type of the UI is 72h, its UIID is 2 DDO-DD9 Device Indicate the Designator device's 10 least significant Device Designator bits S/DSIO-S/DSIl Source/Destinati Indicate the on Subnet subnet of the UI/G Identifier that diagnoses the device C6MIDO - C6MID9 Class 5 Message reserved for a = ID16-ID25 ID LSb/Transfer total of 1024 Protocol possible message _IDs in this class Some messages sent over the RSBus 180 may expect a response. In some cases, the sender expects the response immediately, meaning as soon as the hardware and communication protocol allow the transmission of the 5 response. Such messages are referred to herein as queries. Queries generally have various timing constraints associated therewith. One embodiment of a set of rules is described below that may apply to query messages for most purposes. 10 Message Response Time: Generally messages are to be sent without delay by the sending local controller 290. In many cases it is preferable if a response to a query is generated in 100 ms or less. This means that upon receipt of a query, the responding local controller 290 nrn *)y I - 38 should within 100 ms place a response into its CAN transmit buffer. In many cases the response will not be sent within 100 ms, as the response timing is generally dependent on the traffic conditions on the bus and the 5 message's priority. In one exception to this general rule, in the SUBNETSTARTUP state the local controller 290 is generally configured to wait 100 ms before it attempts to respond to the SCCoordinator message. Thus, the response 10 will be placed in the transmit buffer at a time greater than 100 ms after receipt of the query. Other exceptions to the general response timing rule may be made as desired. Message Resend: A local controller 290 may be 15 configured to resend a message when a correct reply to the message is not received within the expected timeout period. The timeout period may be set to any non-zero value, e.g., about 1 second. If the message is resent after an initial message, and no response is received 20 within the timeout period after the subsequent message, the local controller 290 may attempt to resend the message again. If a response to the third attempt is not received within the timeout period, the local controller 290 may be configured to cease further resending of the 25 message. Of course, more or fewer attempts may be made before ceasing to send the message. In some embodiments, the local controller 290 may send an alarm message identifying the Equipment Type of the unresponsive device, or act in any other way desired. 30 Subnet Controller Monitoring: In some embodiments, the aSC 230a sends a periodic message to other devices on the RSBus 180 that indicates the aSC 230a is present and functioning normally. This message is referred to for nr 7)_ I - 39 convenience as a "Heartbeat" message, e.g., aSCHeartbeat. Each enabled local controller 290 may listen to the aSCHeartbeat message and, when the message is not detected for a specified listening period, may 5 take a specified action. In one embodiment, the local controller 290 may issue an alarm when the Heartbeat message is absent for more than three times its usual send period, e.g., three messages are missed. In some embodiments, the local controller 290 also ceases 10 operation and returns to a default state. Timing Accuracy: Each local controller 290 typically includes an oscillator to provide a timing reference. Each oscillator is preferred to conform to the accuracy for systems with bus speed of up to 125 kbaud, as defined 15 in section 9.1 of the Bosch CAN 2.OB specification. This specification defines resonator accuracy over the entire temperature range and all environmental conditions, including aging, to be 1.58%. In some embodiments, a maximum additional ±200 ps tolerance may be accommodated 20 without notable system degradation. In some cases, the tolerance of the device oscillator may be made more stringent when real-time clock functions are provided. RSBus IDs Header File: The local controllers 290 may be provided by numerous manufacturing suppliers. To 25 promote uniformity of configuration of the various local controllers 290, a system integrator may provide a uniform header file that the suppliers include in firmware controlling the operation of the local controller 290. It is generally preferable that the 30 suppliers use the uniform header file without modification in furtherance of the objective of uniformity of the integrated devices. In an embodiment, - 40 the uniform header file contains all RSBus Message IDs for all messages, including the class of each message. In an embodiment, the file also contains the most current parameter and feature numbers as well as the system wide 5 alarms. In some cases, the alarms, features, parameters and messages are identified by their string names in all caps format, with a prefix according to the type. Thus, e.g., alarm names may be prefixed with a lower-case letter "a", feature names may be prefixed with "f", 10 parameter names with "p" and message names with "mIDx_" when defining the message ID from a class x and "mc" when defining the message class. In a specific example for illustration purposes only, a class 3 message FOO with a message ID of 0x100 15 may be defined as follows: #define mcDEVICEFOO 3 #define mID3_DEVICEFOO Ox100 The file may include the following sections: -Own Alarm IDs - includes Alarm IDs for all 20 Alarms generated by the device * Parameter IDs - includes Parameter IDs for all parameters sent (owned) and received by the device eFeature IDs - includes Feature IDs for all 25 parameters sent (owned) and received by the device *Own User Text IDs - includes all User Text IDs stored by the device -Sent/Received Message IDs - includes message 30 IDs for all messages sent and received by the device r) r1 '7 11 - 41 .Sent/Received Message Classes - includes message classes for all messages sent and received by the device eOwn Alarm Texts - includes installer text in 5 all device supported languages for all alarms owned by the device *Own Feature Texts - includes installer text in all device supported languages for all features owned by the device 10 *Own Parameter Texts - includes installer text in all device supported languages for all parameters owned by the device eOwn Feature Send/Receive Matrix - defines whether the particular Feature is sent and/or 15 received by the device .Own Parameter Send/Receive Matrix - defines whether the particular Parameter is sent and/or received by the device -Own Message Send/Receive Matrix - defines what 20 states each message is sent and/or received by the device Message Bit Timing: Bit timing of the local controllers 290 may be specified for uniformity of operation. In an embodiment, the local controllers 290 25 configure the CAN bit timing as follows. The local controller 290 timing oscillator produces a periodic signal with a period referred to as a time quantum (TQ). In some embodiments, one bit has a period of 25 TQ. Thus for a timing oscillator having a period, or TQ, of about 30 1 us, the bit rate is about 40 kBaud. A local controller 290 may sample the data on the RSBus at a time related to - 42 the TQ. In an embodiment, there the local controller 290 uses a delay time of 8 TQ. The bit is sampled between the 17th and 18th TQ of the bit. If multiple sample points are selected, they may be centered on the transition from 5 17th to 18th TQ. If the chosen CAN platform does not support the clock divider that allows 25 TQ per bit timing, it may be preferred to use a setting with the highest number of TQs per bit, preferably not greater than 25. Delay time 10 should be adjusted to 32% of the bit duration, and the sample points at or centered on 68% of the bit duration. Any of the local controllers 290 in the network 200 may be reset by cycling the power thereof. The local controller 290 is typically configured to execute a 15 power-up routine that places the local controller 290 in a state ready to be configured via messages and thereby begin normal operation. However, among the many advantages of the communication protocol of the disclosure is the ability 20 to implement an efficient method of resetting the local controllers 290 on the RSBus 180 without cycling power to the devices. In an embodiment, a software reset may be issued upon a timeout when a local controller 290 enters the bus off state as described earlier. 25 In another embodiment, the SC 230 resets a local controller 290 using a combination of two messages. A first reset message commands the local controller 290 to prepare for a reset. Optionally, the local controller 290 may respond to the first message with a message, e.g., 30 DEVICEWaiting forReset, indicating that the local controller 290 is waiting for a reset message. The SC 230 sends a second reset message instructing the local controller 290 to reset. The local controller 290 may be 111-1 C 1 ) -1 - 43 configured to only reset in response to the second message if the second message is received within a predetermined time period after the first message, e.g., one minute. If the second message is not received within 5 the predetermined time period, the local controller 290 may resume normal operation and ignore any reset messages received before another message to prepare to reset. In some cases the first and second messages may respectively instruct multiple local controllers 290 to prepare for 10 reset, and to reset. In another embodiment, the local controller 290 is configured to be placed in a "HARDDISABLED" and a "SOFTDISABLED" state. The HARDDISABLED state may be initiated by a user via a message from the UI/G 250. In 15 some cases, this aspect provides the ability to enable or disable a local controller 290 without physically locating the local controller 290. This may be particularly advantageous when the local controller 290 is a logical device, the location of which may be 20 difficult to immediately determine, when expedient disabling of the local controller 290 is desired. While in the HARDDISABLED state, the local controller 290 may be configured to monitor the RSBus 180 without transmitting messages thereover. However, while 25 in this state the local controller 290 may not send messages to other device, nor may the local controller 290 perform any control of an associated demand unit 155. The UI/G 250 may send an appropriately configured message to the local controller 290 instructing the local 30 controller 290 to enter or exit the HARDDISABLED state. These messages may be, e.g., class 6 messages. When the local controller 290 receives a message altering its HARDDISABLED state, it may respond by issuing an 1)I ) C 1" 3 1 - 44 acknowledgment over the RSBus 180, e.g., via a DEVICEUI/GEnable_Acknowledge message. Subnet controllers 230 may monitor these messages to track the state of enablement of the various local controllers 290 5 on the RSBus 180. When the local controller 290 is hard enabled, it may reset itself and enter a CRC check mode. The HARDDISABLED state is persistent, meaning that the local controller 290 remains in the HARDDISABLED state until the user takes an action to send an enable 10 message. In various embodiments the state of enablement is logged in the NVM 320 associated with each physical or logical local controller 290. Thus, the state of enablement, including the condition of being disabled, is remembered by the local controller 290 after reset. 15 In the SOFTDISABLED state, the local controller 290 may continue to respond to messages from the SC 230, but may not execute any control functions. The message may be of a reserved type that instructs one or more local controllers 290 to proceed to a startup state. The local 20 controller 290 may respond in such cases by issuing a message alerting the SC 230 that the local controller 290 is starting up. In various embodiments the state of enablement in the SOFTRESET state is stored in the RAM 320. Thus, the state of disablement in the SOFTRESET 25 state may be cleared upon reset of the system 100. The SOFTDISABLED state may be cleared when the local controller 290 is reset. The aSC 230a may implement a soft-disable of a local controller 290 when the local controller 290 is "alien" to the subnet, e.g., 30 unrecognized as a properly initiated local controller 290. The aSC 230a may also soft-disable a local controller 290 that is determined to be malfunctioning.

- 45 In some embodiments, entry of the local controller 290 to a privileged operating mode may be controlled by messages issued by a special-purpose command interface. One such mode is an OEM programming mode. The OEM 5 programming mode may be used to download configuration data to the local controller 290. Configuration data may include, e.g., serial and model numbers, unit capacity, etc. Such information may be stored in non-volatile memory of the local controller 290, e.g., the NVM 320. 10 Another privileged operating mode is an OEM functional test mode. This mode may provide the ability to test the local controller 290 using, in addition to the messaging protocol, a special data sequence input to a test port that may be separate from the communication 15 capability of the controller 290. For example, the command interface may send a demand message to and receiving status information from the local controller 290 over the RSBus 180, as discussed more fully below. In some embodiments, a special command sequence from 20 a standard UI/G 250 may be used to implement either privileged operation mode. Use of these modes may be restricted by password protection if desired. When the HVAC system 100 is reset or powered up, the local controllers 290 on the subnet are configured in 25 various embodiments to establish an initial operating state of the system 100. One aspect includes configuration of one or more SCs 230 of the subnet of the network 200, e.g. As described further below, each SC 230 enters a SUBNETSTARTUP state upon power-up. During the 30 SUBNETSTARTUP state, the one or more SCs 230 negotiate for the control of the subnet. This negotiation is based on a set of features and parameters of each SC 230, and is designed to ensure that the best SC 230 available 1111'1 -I~ n 1 - 46 controls the subnet. After this negotiation is completed, the SC 230 that is selected by the negotiation process becomes active, or in other words, becomes an aSC that thereafter takes firm control of the subnet. At that 5 point the SC 230 places the subnet in a CONFIGURATION mode or a VERIFICATION mode, and proceeds to assign or reassign Equipment Types and Subnet IDs to the local controllers 290 on the subnet. In the CONFIGURATION mode, a SUBNETSTARTUP process 10 serves to configure the subnet to an operational state. In the VERIFICATION mode, the SUBNETSTARTUP process verifies that a current subnet configuration matches a subnet configuration set up previously during an initial configuration. It is possible to add new devices to the 15 subnet during a Configuration routine executed only when in the CONFIGURATION mode. The VERIFICATION mode may be similar to the CONFIGURATION mode, with two differences as follows. First, in some embodiments the aSC 230a reassigns the same Equipment Types and Subnet ID numbers 20 to the local controllers 290 as were assigned thereto during the last initial configuration. Second, the VERIFICATION mode may be configured to exclude the registration of new devices on the network. As described further below, the CONFIGURATION mode or the VERIFICATION 25 mode may be indicated by values of a CFO and a CFl flag, defined below, of the one or more SCs 230 present in the subnet. FIG. 12 illustrates a state diagram of an embodiment of a SUBNETSTARTUP process, generally designated 1200, 30 that is configured to run on a local controller 290. In various embodiments the process 1200 is implemented as a finite state machine (FSM). In some embodiments the FSM is only implemented on local controllers 290 that are not 1)C1 C 72 1.

- 47 a subnet controller during the process 1200. In some embodiments, every local controller 290 that is not an SC 230 runs a FSM machine consistent with the process 1200. The process 1200 may execute in response to messages sent 5 by the SC 230. The process 1200 begins with a reset state 1210. As mentioned previously, the reset state may be reached from a power-up condition, another device state (such as a check of the NVM 320) or a reset command from a 10 controller, e.g. the aSC 230a. The process 1200 advances to a state 1220, designated DEVICEPRESTARTUP. In an illustrative embodiment, the state 1220 includes a plurality of configuration events that ends with the local controller 290 sending a message over the RSBus 180 15 indicating the local controller 290 is ready to start. This message is referred to for convenience as DEVICEStartup. After the state 1220, the process 1200 advances to a state 1230, designated WAITTOBEASSIGNED. The state 1230 includes a plurality of configuration 20 events that ends with the local controller 290 receiving a message from the aSC 230a commanding a change to an operational state, referred for convenience as aSCChangeState. Upon receiving the aSCChangeState message, the process 1200 advances to a state 1240 and 25 exits. Note that in all states the local controller 290 can still respond to a Class 6 diagnostic message. Thus, from any state, a message may force the process 1200 to the HARDDISABLED state 1250 or to the reset state 1210. The 30 process 1200 illustrates an example in which the process 1200 enters the HARDDISABLED state 1250 from the state 1220. The process 1200 remains in the state 1250 until the local controller 290 receives an appropriate message - 48 as described previously. The process 1200 may then advance to the state 1210, from which the local controller 290 may begin the initialization process again. 5 The process 1200 also illustrates an example in which the process 1200 enters a state 1260 SOFTDISABLED state from the state 1230. The process 1200 may remain in the state 1260 until the local controller 290 is reset as previously described. The process 1200 may then advance 10 to the state 1220. In some embodiments, the local controller 290 is configured to remain, during the state 1220, in a listen only mode for a predetermined period, e.g., at least about 5000 ms. In the listen-only mode, the local 15 controller 290 monitors messages sent over the RSBus 180, but does not initiate any messages. After the listen-only period expires, the local controller 290 may optionally wait an additional startup delay period. After the optional additional delay, the local controller 290 may 20 send a DEVICEStartup message over the RSBus 180, and may then monitor the RSBus 180 for any messages that indicate other devices on the RSBus 180 failed to receive the startup message correctly. In some cases, the local controller 290 may initiate 25 its startup message before the end of the 5000 ms listen only period. In one embodiment, the local controller 290 receives an SCCoordinator message. In this case, the local controller 290 sends a startup message immediately after powering up. In this context, immediately means 30 after about 100 ms plus an additional delay derived from the Device Designator. In some such cases, the message is not received successfully by at least one other local controller 290, resulting in a Bit Error event on the - 49 RSBus 180. If the Bit Error is detected, then the device may wait a specified period, after which it resends the startup message. A specific resend delay period may be selected for a particular local controller 290. In 5 various embodiments the resend delay reduces the probability of message collision on the data bus 180. An algorithm that determines this resend delay time as a function of the Device Designator may compute the resend delay period as described further below. 10 In various embodiments the system 100 is configured to allow multiple devices of the same type to start communicating on the network 200. These embodiments allow seamless plug-and-play configuration even when the bandwidth of the data bus 180 is limited. The following 15 example illustrates principles of these embodiments, and is presented by way of illustration without limitation. In one embodiment the DeviceStartup message ID is unique to each type of device. The message data field of the DeviceStartup message may be identical to the data 20 field of the DeviceDesignator message. These messages may be Class 5 messages, and in such cases they may have RSBus message IDs that include an offset number and a five bit order number shifted left by one, so as not to interfere with the CAN ID bit ID13 used to indicate the 25 transport protocol. In these messages the order number is defined for a particular system device 410 as the five least significant bits of the Device Designator (DD) of that system device 410. In some embodiments using a Class 3 message that includes the 5-bit order number, the 30 position of the order number in the message ID is not shifted by one. For the case of the aSC 230a, the order number can also be a number calculated from the number of 'IC ' -1 7 'J I - 50 other subnet controllers, typically one or more instances of the iSC 230i, detected on the subnet. In a nonlimiting example, the DeviceStartup message is Oxl8O, and the last byte of the DD is 0x45, then the 5 message ID of the DeviceStartup message is 0x180 + (0x45 & 0xlF) = Ox18O + OxOA= Oxl8A. As described further below, a base delay time may be scaled by the value of the order number. The occurrence of a bit error when a system device 410 sends a 10 DeviceStartup message indicates that two devices 290 simultaneously attempted to publish a message on the data bus 180, referred to herein as a message collision, or more briefly, a collision. When a collision occurs, the devices delay resending the DeviceStartup message for a 15 unique period derived from the order number. Thus in various embodiments the presence of the order number advantageously reduces the probability of collisions by the factor 2 b, where b is the number of bits of the order number. In the embodiments described above, 20 the collision probability is reduced to about 3% of the collision probability that would otherwise be present. After the local controller 290 successfully sends its startup message, the local controller 290 may wait for a Startup Response message from the aSC 230a. The 25 Startup Response may be configured to provide a node assignment to the local controller 290. A node assignment message is referred to for discussion purposes as an aSCDEVICEAssignment message. The aSCDEVICEAssignment message may be sent by the aSC 230a from its subnet. This 30 message may contain information regarding the subnet that the local controller 290 may need to operate properly. Information conveyed by aSC DEVICE Assignment may additionally include the Equipment Type assigned to local ') C 'M1'7~ 11 - 51 controller 290, and other flags. After the local controller 290 receives the aSCDEVICE message, the local controller 290 may send an acknowledgement message over the subnet of the network 200 it has been assigned to. 5 The message may include, e.g., the Equipment Type of the local controller 290. If a local controller 290 does not detect a startup response message addressed to it within 5 minutes after it is initiated, the local controller 290 may repeat its 10 startup message. In some embodiments, the local controller 290 repeats the startup message every 5 minutes until the local controller 290 successfully receives an Equipment Type and Subnet ID assignment, e.g., via a aSCDEVICEAssignment message. The local 15 controller 290 may send an acknowledgement message indicating it is configured and ready to operate normally. In some embodiments, all local controllers 290 are required to receive an aSCDEVICEAssignment message before sending an acknowledgement. In some cases, 20 exceptions may be made to this requirement where system design considerations warrant. In some cases, the local controller 290 was assigned an Equipment Type and a Subnet ID in a previous system startup. In some embodiments, the local controller 290 25 retains the previously assigned values. In other cases, the local controller 290 was not previously assigned an Equipment Type and a Subnet ID, such as when the local controller 290 is initially added to the system 100. In some embodiments, a local controller 290 that has not 30 previously been assigned an Equipment Type and a Subnet ID are assigned a default value. The default value of the Equipment Type may be a lowest Equipment Type for the specific device. The default Subnet ID may be, e.g., 0. ') C ) C1 '7 11 - 52 When a subnet starts up, an SC 230 may publish an SCCoordinator message to the data bus 180 to coordinate control of the subnet with any other instances of the SC 230 on the subnet. When the local controller 290 receives 5 the SCCoordinator message it may respond with a DEVICEStartup message if the local controller 290 is in the SUBNETSTARTUP or SOFTDISABLED states, or in an OEM Test state described above. Otherwise the local controller 290 may respond with the 10 DEVICEDeviceDesignator message. For example, if the local controller 290 sees the SCCoordinator message after powering up, it may respond with the DEVICEStartup message. Then, the local controller 290 may be assigned an Equipment Type and 15 Subnet ID by an aSCDEVICEAssignment message, and may then receive an aSCHeartbeat message. If the local controller 290 receives another SCCoordinator message, the local controller 290 may again respond with the DEVICEStartup message, because it has not cleared the 20 SUBNETSTARTUP state since the last reset. If the local controller 290 is assigned and changes state to, e.g. a COMMISSIONING state and then receives another SCCoordinator message, the local controller 290 may respond with a DEVICEDeviceDesignator message. If the 25 local controller 290 is assigned for the second time, but remains in the SUBNETSTARTUP state when yet another SCCoordinator message arrives, it may respond with a DEVICEStartup message, as it is no longer necessary to remember the previous state. 30 Restated from the perspective of the aSC 230a, if the aSC 230a receives a DEVICEDeviceDesignator message, it knows that the local controller 290 has not recently been reset. If the aSC 230a receives the DEVICEStartup O)ri 1 71 - 53 message, it knows that the local controller 290 has not been assigned and has not changed state since last hardware or software reset of the local controller 290. FIG. 6B illustrates an embodiment in which a link 5 relay is used to selectively isolate the subnet 615 from the subnet 620. In a conventional communicating HVAC system all devices share a common communicating bus. During system installation and configuration special care must be taken to ensure that corresponding equipment from 10 same HVAC system is matched. Installation becomes more cumbersome and prone to error as the number of connected systems increases, and as the number of components in the total system increase. Moreover, if a bus error occurs, such as a short circuit between bus wires, the entire 15 network may be disabled. In the embodiment of FIG. 6B, the subnet 615 and the subnet 620 may be selectively isolated from each other using a switch 699 such as a relay. Two systems, one corresponding to each subnet 615, 620 may be installed, 20 configured and tested separately. At a proper time the aSC 230a in each subnet 615, 620, for example the SC 662 and the SC 682, may link its subnet to another subnet by actuating the switch 699. Advantageously, and in contrast to conventional HVAC systems, if a communication bus 25 failure is detected, the aSC 230a may disconnect its subnet from the network 200 to localize the problem. The aSC 230a may put the switch 699 in a local mode (e.g., isolating its subnet) as soon as immediately upon receiving a SCCoordinator message from any subnet, or 30 upon receiving an SCStartup message from an aSC 230a on the same subnet. After repair, the aSC 230a may be instructed via an appropriately configured message to reconnect to the network 200. Thus, at least some HVAC - 54 services may be maintained even if one subnet is rendered inoperable by a failure of the data bus 180. Turning now to FIGs. 13A and 13B, illustrated is a method generally designated 1300A that may run on a 5 subnet controller, e.g., the SC 230, during subnet startup, e.g., during the SUBNETSTARTUP state. FIG. 13A, presenting a summary view of the method 1300A, is described first. FIG. 13B, described afterward, presents a more detailed flow chart 1300B of the method. 10 First addressing FIG. 13A, the method 1300A begins with a reset state 1301. The state 1301 may result from power-up or an appropriately configured reset command. A state 1303 provides pre-startup activity, e.g., startup messages to system devices 410 in the network 200. A 15 state 1309 provides post-startup activity, e.g., arbitrating the aSC 230a. In some cases a system device 410 will be placed in a hard disable state 1307, for example when pre-startup activity indicates that the system device 410 is not functioning properly. After the 20 post-startup state 1309, an SC 230 that is assigned the role of the aSC 230a during arbitration during the state 1309 proceeds to an active-coordinator state 1313. The aSC 230a may perform system administrative tasks in the state 1313. After the aSC 230a performs such 25 administrative tasks the method 1300A proceeds to state 1379 at which point the aSC 230a broadcasts an aSCheartbeat message, indicating that the aSC 230a has asserted control over its subnet. The method 1300A terminates with a state 1399, from which the aSC 230a 30 continues with system control functions. An SC 230 that does not become the aSC 230a advances in the method 1300A to a passive-coordinator state 1315. The SC 230 entering the state 1315 is assigned the role ') ')C17 ' 1 - 55 of iSC 230i. The iSC 230i performs various tasks in the state 1315 and may then advance to an inactive state 1355. In various embodiments the iSC 230i continues to receive messages in the inactive state 1355, and may 5 perform some functions such as storing backup parameters from other system devices 410, but does not exert control over the subnet. In some cases the iSC 230i may advance to a soft disable state 1351, e.g. if commanded to do so by a suitable formatted message. 10 As described, FIG. 13B presents a more detailed flow chart of the method 1300A, generally designated in FIG. 13B as a method 1300B. During the pre-startup state 1303, the SC 230 may execute a step 1305, in which it may send several SCstartup messages according to the various 15 embodiments described herein. In the post-startup state 1309, the SC 230 may perform the previously describe arbitration in a step 1311. If the SC 230 becomes the aSC 230a, it may in various embodiments be the first of multiple instances of the SC 230 on the subnet to 20 broadcast an SCcoordinator message. In a step 1317, the SC 230 determines if it is indeed the first to broadcast the SCcoordinator message. If so, the SC 230 enters the active-coordinator state 1313, wherein it performs various administrative tasks 1357-1375. The SC 230 then 25 advances to the heartbeat-out state, wherein it may broadcast the aSCheartbeat message in a step 1377. The SC 230, now referred to as the aSC 230a, may perform various configuration steps 1381-1391 before exiting the method 1300B with an exit state 1399. 30 If in the step 1317 the SC 230 determines it is not the first SC 230 to send an SCcoordinator message, it branches to the passive-coordinator state 1315 described previously. The SC 230 may perform various configuration - 56 steps 1319-1347. In a step 1349, the SC 230 may determine that it is disabled. If so, the SC 230 may enter the soft-disabled state 1351 and remain therein until a reset. If the SC 230 is not disabled, it may enter the 5 inactive state 1355, at which point it is referred to as the iSC 230i. The method 1300B exits with an exit state 1398. FIG. 13C presents without limitation an example embodiment of states of a state machine configured to 10 implement a subnet controller startup process. Those skilled in the pertinent art will appreciate that the illustrated embodiment is one of many that may be used, and that such others are included in the scope of the disclosure. 15 In an advantageous embodiment, the controllers SC 230 do not queue inbound or outbound messages. Configuration times discussed below are presented without limitation for this case. Moreover, if a message is scheduled to be sent out at a specified time, in some 20 embodiments only one attempt to send the message is made. The SC 230 does not automatically attempt to resend the message in such embodiments. However, the SC 230 may attempt to resend the message when a new specific time is scheduled to send the message after the send failure. 25 In an embodiment, the Subnet Controller startup sequence begins with the SC 230 issuing a SCStartup message. The message may be sent at a consistent period after the SC 230 emerges from a reset state. In an example embodiment, the period is about 3000 ms plus a 30 supplemental delay period derived from the Device Designator. After performing a functional test of local NVM, e.g. the NVM 320, each SC 230 on the RSBus 180 listens - 57 for startup messages from other local controllers 290. The SC 230 records all Device Designators and configurations, e.g. Equipment Types and Subnet IDs, for all local controllers 290 on the network that send their 5 startup messages. After the supplemental delay period, e.g., about 1000 ms, the first SC 230 may attempt to send a second message, e.g., a SCCoordinator message. In an example case in which there is no other traffic on the RSBus 180, 10 the SCCoordinator message appears on the RSBus 180 after about 1000 ms plus the time required to send the SCStartup message onto the RSBus 180. Of course such timing is subject to imprecision determined by system level design consideration. If the first SC 230 15 successfully broadcasts the SCStartup message, it becomes the active coordinator, e.g., the aSC 230a, and proceeds to coordinate the system configuration. If the first SC 230 fails to send the SCStartup message, or a second SC 230 successfully sends a message first, then 20 the second SC 230 becomes the aSC 230a and the first SC 230 enters a PASSIVECOORDINATOR state and becomes an inactive subnet controller, e.g. the iSC 230i. The SC 230 may determine that it is a best subnet coordinator, e.g., has priority over other available 25 instances of the SC 230 on the subnet 200, by querying such other instances to determine relative capability and features. The SC 230 may additionally take into account factors unrelated to features and capability. Such determination may include the following factors, 30 presented by way of example without limitation: 1) Subnet Priority Level (SPL) (akin to a user selectable override) - the operator can chose to use a '7 R 1 -1 - 58 particular SC 230, even if it is deemed less advanced than others on the subnet 2) Device Product Level (DPL) (such as different tiers of capability based on cost) - an SC 230 with 5 greater features or capability may be indicated by a product level number, with a greater number indicating a more capable SC 230 3) Its Protocol Revision Number (PRN) - a recent design revision of the SC 230 may be indicated by a 10 higher revision number 4) Its Device Designator or Serial Number (DD/SN) a greater number of the Device Designator or serial number may be generally associated with a more recently produced SC 230, which may be presumed to be more capable 15 In some embodiments, the determination is made considering the above-listed factors in the order indicated. Thus, a first SC 230 with a greater DPL than a second SC 230 may take priority even if the second SC 230 have a greater PRN or DD/SN. In some embodiments, the SPL 20 overrides all other factors. In some embodiments if all factors are otherwise equal, then the SC 230 with a greater Device Designator will take priority over any SC 230 with a lower Device Designator. If the SC 230 determines that it is the most 25 qualified SC 230 on the subnet 200, it proceeds to assume control of the subnet 200 by first issuing a SCReady_ ToTakeOver message. After a predetermined period, e.g. about 1000 ms, the aSC 230a issues the aSCHeartbeat message. Alternatively, if the aSC 230a 30 determines it is not the most qualified SC 230 on the subnet 200, it will pass a token to the SC 230 that is determined to be the most qualified SC 230. The SC 230 ')C' -1'7 7 1 - 59 passing the token becomes an inactive iSC 230i, and the SC 230 receiving the token becomes the aSC 230a. When the aSC 230a assumes control of the subnet of the network 200, it determines if the subnet of the 5 network 200 is in the CONFIGURATION mode or in the VERIFICATION mode and proceeds to configure the system accordingly. If the subnet of the network 200 is in the VERIFICATION mode, the aSC 230a issues alarms for all missing and new local controllers 290. New local 10 controllers 290 will be excluded from the subnet of the network 200 and placed in the SOFTDISABLED state. The aSC 230a may also check the validity of the configuration of the subnet of the network 200 and issue appropriate alarms if needed. If the subnet of the network 200 is 15 configured correctly, the aSC 230a concludes the SUBNETSTARTUP process by issuing an aSC_ChangeState message. In some cases there may be more than one SC 230 on a single subnet of the network 200 capable of controlling 20 the subnet. In this case, an arbitration algorithm may arbitrate among the eligible SCs 230 to determine which SC 230 will assume the role of the aSC 230a. The algorithm may consider various factors, including, e.g., for each eligible SC 230 the CFl flag setting, defined 25 below, a Subnet Priority Level, a Device Product Level, and a hardware revision number. A Subnet Priority Level may be, e.g., an identifier that allows for overwriting the priority level of an SC 230. In some embodiments the Subnet Priority Level of each SC 230 is set to 0 in the 30 factory and can only be changed by a specific sequence of messages sent by the Interface/Gateway 250. The Device Product Level may be, e.g., a designation of a level of feature configuration, such as Signature, Elite or Merit - 60 product lines. After the system 100 is configured, all aSCs 230a run the normal operation of their respective network subnets. In various embodiments each SC 230 in the system 100 5 stores the Device Designators of all other configured SCs 230 in the system 100. Each SC 230 may also store its last active, inactive or disabled state. Recalling that each message includes a message ID, the ID of the DEVICEStartup message is unique to the 10 message being sent. The message data field of the local controller 290 may be identical to the data field of DEVICEDeviceDesignator messages sent by that local controller 290. Since these messages may be Class 3 messages, as described previously, they may have RSBus 15 Message IDs that are formed from an offset number and a 5-bit Order Number. In an example embodiment, the Order Number of a particular local controller 290 is the 5 least significant bits of the Device Designator of that local controller 290. 20 For example, if the DEVICEStartup message is 0x700 and the last byte of Device Designator is 0x45 then the message ID of the DEVICEStartup message may be 0x700 + (0x45 & 0xlF) = 0x700 + OxO5 = 0x705. For Class 5 messages that include the 5-bit Order 25 Number, the position of the Order Number in the message ID may be shifted left by one position so as to prevent interference with the position of the Transport Protocol bit C5MIDO/TP. The Order Number of the SC 230 may also be a number calculated from the number of other SCs detected 30 on the subnet. All startup messages, e.g., DEVICEDeviceDesignator and SCCoordinator messages, can contain seven Configuration Flags, CFO-CF6. The encoding of these flags C 7 ) 1 - 61 may vary depending on the device type. For example, the flags of the SCs 230 may be encoded differently than other local controllers 290. In some embodiments, for the local controllers 290 5 that are not an SC 230 the flags may be encoded as follows: CFO: 0 if the local controller 290 has not been configured (e.g. is a new device) 1 if Installer Test Mode tests complete 10 successfully, or upon receipt of an aSC_ChangeState message indicating transition to Normal Operation CF1: 0 if the control is intended for permanent use 15 1 if it is attached temporarily CF2: 0 if the local controller 290 cannot be flashed over the RSBus 180 1 otherwise CF3: 0 if the local controller 290 is hard 20 disabled/not-communicating 1 if the device is hard enabled/communicating CF4: 0 if the local controller 290 is soft disabled, or was soft disabled immediately 25 prior to sending this message, when this message is sent in the Subnet Startup state 1 otherwise CF5 0 if the local controller 290 is a factory 30 installed part 1 if the local controller 290 is a replacement part - 62 CF6: 0 if the local controller 290 has failed the Data CRC check 1 otherwise In some embodiments, for the local controllers 290 5 that are an SC 230 the flags may be encoded as follows: CFO: 0 if the SC 230 has not been configured, e.g. is a new device 1 upon successful completion of Installer Test Mode tests 10 CFl 0 if the SC 230 does not recognize any indoor units on the subnet 1 if the SC 230 recognizes at least one indoor unit on the subnet CF2 0 if the SC 230 cannot be flashed over 15 RSBus 180, 1 otherwise CF3 0 if the SC 230 is hard disabled/not communicating 1 if the SC 230 is hard 20 enabled/communicating, CF4 0 if the Subnet Controller is soft disabled, or was soft disabled immediately prior to sending this message 1 otherwise 25 As described above, the CFO flag may be used as an indication of the whether an associated local controller 290 has been configured. The CFO flag may be cleared (0) in all local controllers 290 under the following circumstances, e.g.: 30 -When all device parameters revert to default values, such as via a specific diagnostic inquiry/command. ') C71 -7 1 - 63 -When the device is restored to factory defaults via a specific diagnostic inquiry/command. -When the device loses its internal NVM 5 settings, as described below. At any time and regardless of the CFO flag setting, if the local controller 290 enters the COMMISSIONING state and either the UI/G 250 or the aSC 230a attempt to change settings on the local controller 290, the local 10 controller 290 complies with the changes. In various embodiments, the system 100 enters the CONFIGURATION mode or the VERIFICATION mode described previously. In an embodiment the system 100 may only enter the CONFIGURATION mode when the CFO flag is reset 15 (0) for all native SCs 230 on the subnet. A non-native SC 230 may enter the CONFIGURATION mode when either its CFO bit or the CFl bit is reset. As used herein a native SC 230 is an SC 230 that was present in the subnet during the most recent subnet configuration. A non-native SC 230 20 is an SC 230 that was not present, and was this not detected and is not remembered by other instances of the SC 230 in the subnet. As described above, the CF1 flag is set when it recognizes a configured indoor unit on its subnet 200. If these conditions for entering the 25 CONFIGURATION mode are not present, the system 100 may be placed in the VERIFICATION mode by a SC 230 on the subnet 200. If a Bit Error is detected when sending the startup message, e.g., DEVICEStartup, the message is resent 30 after a predetermined delay time in various embodiments. The delay time may be computed by an algorithm that employs the Device Designator. In one embodiment, the Device Designator field is parsed into 4-bit portions, ' 'C 1 '7 I - 64 each being a contiguous subset of bits of the Device Designator. If the Device Designator field is 32 bits, e.g., eight successive portions are thereby obtained. For brevity the bits of the Device Designator field are 5 represented as DD[0]-DD[31]. In an example, the value of each 4-bit portion is incremented by 1, with the result being multiplied by 4 ms to determine a delay time associated with that portion. In an embodiment, the eight successive portions are associated with delay times as 10 indicated below: eDD[O]-DD[3]: Startup Delay eDD[4]-DD[7]: First Resend Delay eDD[8]-DD[1l]: Second Resend Delay eDD[12]-DD[15]: Third Resend Delay 15 *DD[16]-DD[19]: Fourth Resend Delay -DD[20]-DD[23]: Fifth Resend Delay -DD[24]-DD[28]: Sixth Resend Delay eDD[29]-DD[31]: Seventh Resend Delay If the message is not successfully sent after the 20 eight attempts, subsequent delivery attempts may continue to be made repeating the eight resend delays. In some cases, the message may be resent up to a predetermined maximum, e.g. 255. If the message is not successfully sent within the predetermined maximum, the local 25 controller 290 may be configured to disengage from the subnet 200, e.g. enter a passive state. The local controller 290 may further be configured to execute the message send/retry cycle again after a predetermined delay period, e.g., about 5 minutes. 30 As described previously with respect to FIG. 5, in some embodiments a single physical device may include multiple logical devices. In cases in which a physical device contains more than one logical device, it may be 7%111 1 - I - 65 preferable to limit all logical devices to be configured to the same subnet 200. Generally each logical device, e.g., the aSC 470, the user interface 480 and the comfort sensor 490, sends out its own DEVICEStartup messages. 5 Generally, logical devices are configured separately by messages sent by the aSC 230a. In the case of a system device 410 that includes multiple logical devices, the aSC 230a assigns the same Subnet Identifier to each logical device. Taking the thermostat 590 (FIG. 5) as an 10 example, the aSC 230a may assign the Equipment Type and the Subnet Identifier to the aSC 510. The aSC 230a may then also assign the same Subnet Identifier to the user interface 520 and the comfort sensor 530 via instances of an assignment message, e.g., aSCDEVICEAssignment. Each 15 logical device may also respond with its own message acknowledging the assignment message, e.g., a DEVICE Assignment_Acknowledge message. As described previously, each local controller 290 may have an associated NVM, e.g., the NVM 320 (FIG. 3). 20 In some cases, the NVM may become corrupted. In various embodiments the contents of the NVM of each local controller 290 are archived by each SC 230 on the subnet of the network 200. Each SC 230 may also archive the last active, inactive and disabled state of each local 25 controller 290. The contents of a corrupted NVM may then be restored using archival copies of the contents stored on any SC 230. Additionally, in some cases a local controller 290 may archive application-specific data on one or more of the SCs 230. For example, a local 30 controller 290 may have associated data values that represent special parameters. During the COMMISSIONING state, the local controller 290 may archive the parameters on the one or more SCs 230. Then, in various - 66 embodiments the SC 230 is configured to restore the contents of the NVM on a local controller 290 that has determined the contents thereof are corrupt. In some embodiments a local controller 290 maintains 5 a local copy of the NVM data. The local controller 290 so configured may recover its NVM data without intervention from an SC 230. The local controller 290 may be configured to restore the contents of its NVM without changing its apparent behavior to other local controllers 10 290 in the system 100. The local controller 290 may be further configured to verify the integrity of the NVM contents before sending a DEVICEStartup message. In an embodiment, when participation by an SC 230 is needed to recover NVM data, the recovery process may be 15 performed by the device itself in conjunction with the aSC 230a. Four example failure modes are described without limitation to demonstrate various features of the embodiment. In a first case, the data stored on the local 20 controller 290 NVM is corrupt, but a locally archived copy is valid. In this case, the device may recover the data from its internal backup in a manner that does not affect its apparent operation as viewed by the other local controllers 290. In an advantageous embodiment, no 25 indication is given to the other local controllers 290, and control of the affected local controller 290 is unaffected. In a second case, the data stored on the local controller 290 NVM is corrupt, but a locally archived 30 copy is not valid, or no copy is locally stored. However, the aSC 230a stores correct values for the device. In this case, the local controller 290 may send a message, e.g., the DEVICEStartup message, sent on Subnet 0, using ') ')C1-7 ' 1 - 67 the default Equipment Type for that local controller 290, with the CF6 flag cleared. It responds to all SCCoordinator messages using the same message until a new Equipment Type and Subnet ID are assigned to it. As 5 long as the NVM data are not recovered the CF6 flag remains reset. Once an aSC 230a takes over, it proceeds to assign the Equipment Type and Subnet ID to the local controller 290 as usual, which the local controller 290 stores internally. The aSC 230a recognizes the local 10 controller 290 using its Device Designator and may assign the same Equipment Type and Subnet ID as previously assigned thereto. The local controller 290 may initially restore NVM data to default values stored in the device flash. The aSC 230a may in parallel enter the 15 COMMISSIONING state to reprogram the local controller 290 with the data from its backup. The local controller 290 will typically replace any default values it may have placed in the NVM with data provided by the aSC 230a. In a third case, the archival data stored on the aSC 20 230a is corrupt. In this case, the aSC 230a may enter the VERIFICATION mode. In this state, the aSC 230a may obtain all data from associated local controller 290 as is normally obtained during verification. In some embodiments, the aSC 230a may instruct the local 25 controller 290 to provide more data than is normally provided during the verification. Finally, in a fourth case, the data stored on the local controller 290 and the archival data stored on the aSC 230a is corrupt. In this case the local controller 30 290 may restore the NVM to default values. The aSC 230a may obtain the default data as described for the third case. 111-n~l"-I - 68 Turning now to FIG. 14, illustrated is a method, generally denoted 1400, of an algorithm that may be employed by the aSC 230a to assign the Equipment Type to such a local controller 290. The method 1400 is 5 representative of cases in which a device has an Equipment Type unknown to the aSC 230a. In step 1405, the aSC 230a receives a startup message, e.g. DEVICEStartup, from a local controller 290 having an unknown Equipment Type. In a branching step 10 1410, the aSC 230a determines if another unknown local controller 290, that has the same Equipment Type as the current unknown Equipment Type, has previously sent a startup message. If not, the method 1400 advances to a step 1415. In the step 1415, the aSC 230a assigns to the 15 local controller 290 the Equipment Type provided by the local controller 290 in its startup message, and then ends with a step 1420. If in the step 1410 the aSC 230a determines in the affirmative, then the method 1400 advances to a step 20 1425. In the step 1425, a variable startET is set equal to the value of the Equipment Type received from the unknown local controller 290 in the startup message. A variable newET is set equal to the value of startET. A variable Increment is set to +1. The method 1400 advances 25 to a step 1430, in which the value of Increment, presently +1, is added to newET. In a decisional step 1435, if it is determined that there is another local controller 290 that has already been assigned the Equipment Type value currently stored 30 by newET, the method returns to the step 1430, where newET is again incremented. If instead it is determined in the step 1435 that there is not a local controller 290 with the Equipment Type held by newET, the method 1400 n *) I - 69 advances to a step 1440, in which the aSC 230a assigns the value of newET to the Equipment Type of the unknown local controller 290. In a decisional step 1445, the aSC 230a waits for an 5 acknowledgement from the unknown local controller 290, e.g., via a DEVICEAssignmentAck message. When the acknowledgement is received, the method 1400 advances to a decisional step 1450, in which it is determined whether the assignment was successful. If the assignment was 10 successful, the method 1400 ends at the step 1420. If in the step 1450 it is determined that the assignment was not successful, the method 1400 advances to a decisional step 1455. If it is determined that the Equipment Type was rejected as being too high, the method 15 1400 advances to a step 1460, in which newET is set equal to startET and the value of Increment is set to -1. The method then returns to the step 1430. If instead in the step 1455 it is determined that the Equipment Type is not rejected as too high, the 20 method 1400 advances to a decisional step 1465 where it is determined if the Equipment Type is rejected for being too low. If the Equipment Type is not rejected as being too low, this condition represents the case, e.g., that there is another device already assigned the Equipment 25 Type value. The method 1400 returns to the 1430 where newET is again incremented. If, on the other hand, it is determined in the step 1465 that the Equipment Type was rejected for being too high, the method advances to a step 1470. The step 1470 establishes that the maximum 30 number of devices is present in the system 100. The unknown local controller 290 is set to a SOFTDISABLED state, and the method 1400 ends with the step 1420. ' 1 '71-1 - 70 In one advantageous embodiment, the disclosure provides for a method of replacing controls in an HVAC system. In some circumstances, a controller, e.g., the UI/G 250, may need to be replaced in an installed and 5 configured HVAC system, e.g., the system 100. Manual configuration and calibration of the new controller by the installer would be time consuming and expensive to the user of the system 100. In an embodiment, settings for the SC 230 are 10 provided by an archived copy by another SC 230 as described previously. Each subnet controller, e.g., the SC 230, stores the Device Designator and equipment serial and part numbers for each device in the network, e.g., the network 200. The Device Designator and equipment 15 serial and part numbers of an original local controller 290 may be assigned and stored on the local controller 290 at a manufacturing or assembly facility, e.g. However, the equipment serial and part numbers may be left blank for a replacement local controller 290. The 20 missing equipment serial and part numbers and a set CF5 flag, as describe above, identify the replacement local controller 290 as such to the SCs 230 on the network 200. The CF5 flag may be provided by the replacement local controller 290 via a DEVICEStartup message, e.g. Thus, 25 the aSC 230a may configure the replacement local controller 290 with all pertinent parameter values, as well as the equipment serial and part numbers, all previously archived from the replaced local controller 290. This approach significantly simplifies the 30 replacement of local controllers 290 on the network 200. In an example embodiment, the aSC 230a categorizes the replacement local controller 290 based on the Device Designator actually stored thereon, rather than based on ~ 1) I r 73 * - 71 the archived Device Designator of the replaced local controller 290. The aSC 230a determines that the replacement local controller 290 is a replacement part by the presence of the set CF5 flag, as described 5 previously, and the lack of a local controller 290 on the subnet 200 that corresponds to the replacement local controller 290. In the VERIFICATION mode, the replacement local controller 290 is placed in a SOFTDISABLED state. The configuration of the replacement local controller 290 10 with the archived data from the replaced local controller 290 is performed during the COMMISSIONING state. Optionally, an alarm may be generated by the aSC 230a indicating that the replaced local controller 290 is missing. 15 In an embodiment, during the COMMISSIONING state the aSC 230a may verify that the replacement local controller 290 is compatible with the replaced local controller 290 with the participation of a user or installer. For example, the aSC 230a may prompt the user to 20 automatically configure the replacement local controller 290 by listing a set of equipment serial and part numbers for each of the replacement local controller 290 and the replaced local controller 290. The user may then be prompted to copy the archived values of all data, 25 including all pertinent parameters and the equipment serial and part numbers onto the replacement local controller 290. If the user accepts, then the configuration data are automatically copied to the replacement local controller 290. In another embodiment, 30 the user declines to automatically overwrite the configuration data of the replacement local controller 290, and may enter desired configuration data via a UI/G 250.

- 72 When a new local controller 290 is added to the subnet of the network 200, this condition may be determined by the aSC 230a by the presence of a reset CF5 flag, and a Device Designator that does not match a local 5 controller 290 already present on the subnet. In such a case, the equipment serial and part numbers are undisturbed in the COMMISSIONING state. However, as before the new local controller 290 may be placed in the SOFTDISABLED state in the VERIFICATION mode. The CF5 10 flag may be protected against casual change. In some cases, the CF5 flag may only be changed in a privileged mode, e.g., an OEM test. In various embodiments of the system 100 normal operation involves the delivery of DEVICEStatus messages 15 and service demand messages by the aSC 230a. A demand message may be expressed in terms of a percent of a full capacity of a demand unit 155. A staged demand unit 155 may round off a percent of demand communicated to it to a value associated with a nearest stage capacity. In some 20 embodiment the aSC 230a is configured to know values associated with the stages of a particular staged demand unit 155, and may provide demand messages consistent with these values. In some embodiments a demand message targeting a demand unit 155 that includes a blower or 25 similar device contain a blower override value. The demand unit 155 may change a blower speed from a default value associated with the requested demand level in response to the override value. An override value of 0 may indicate that the default may be used. 30 In some embodiments, a heating demand is mutually exclusive of a cooling demand. In cases of simultaneous demands that are not prohibited, a blower speed may default to a highest CFM value of the demands associated nr c ") I - 73 with the multiple demands. In one example, the configuration of the system 100 is changed from cool plus blower to blower only. A blower demand message may be sent with a desired blower level, followed by a cooling 5 demand message that causes a compressor to cease operation. In various embodiments, the aSC 230a tracks the availability of capacity of the demand units 155. If for some reason a service, e.g., cooling, provided by a 10 demand unit 155 becomes unavailable, the aSC 230a may clear demand messages that request that service. Each local controller 290 is configured to transmit its own status on the RSBus 180 using the DEVICEStatus message. In various embodiments all DEVICEStatus 15 messages share the same first two bytes regardless of equipment type. These two bytes may contain alarm and service status information. Each bit in the service status byte (service bits) will be '1' if the service provided by the demand unit 155 associated with the local 20 controller 290 is available, or if the local controller 290 sending the message does not know status of the service. The following device status table illustrates the principle: Device Fan Gas Elec- Heat Cooling Humidifi- Dehumidif Heat tric Pump cation -ication Heat Heat Comfort 1 1 1 1 1 1 1 Sensor Furnace 1 1 1 1 1 1 1 Heat Pump 1 1 1 1 1 1 1 Dehumidifier 1 1 1 1 1 1 1 Logical AND 1 1 1 1 1 1 1 )C ) C~1 7) 3 - 74 Each row of the table represents a device status vector maintained by the corresponding system device. Each column of the table represents a potential service provided by the corresponding system device. A potential 5 service is a service that may be provided by the system 100 when the system 100 is appropriately configured. The system 100 need not actually be configured to provide the service. Also, each system device typically only provides a subset of the potential services, and may only provide 10 a single service. [0100] If the service is not available the bits of the service status byte are set to '0'. The aSC 230a receives the service bytes from all the various system devices 410 on the subnet 200 and performs a logical AND (any device 15 sending a '0' will result in the service being unavailable). In an embodiment, each alarm associated with a status bit modifies the status bit when the alarm is active. Thus, for example, an alarm condition of the furnace 120 may result in the associated status bit of 20 the furnace 120 being set to "0" to indicate the furnace is unavailable. The following device status table illustrates the principle: Device Fan Gas Electric Heat Cooling Humidifi- Dehumidif Heat Heat Pump cation ication Heat Comfort 1 1 1 1 1 1 1 Sensor - 75 Furnace 1 0 1 1 1 1 1 Heat Pump 1 1 1 1 1 1 1 Dehumidifier 1 1 1 1 1 1 1 Logical AND 1 0 1 1 1 1 1 Each bit that indicates the unavailability of a service, e.g. "O", may be reset to a state indicating the service is available, e.g., "1" when an alarm condition 5 related the unavailable service clears. The alarm may clear after the expiration of a predetermined interval, e.g. an "alarm timeout", or the alarm may clear if reset by intervention of an operator, e.g., via the UI 240. This method advantageously simplifies maintenance of 10 the system 100 by rendering it unnecessary to modify the device status in many cases when a system device is replaced. The method also eases system expansion by the manufacturer. Each alarm may be an event-type alarm or a 15 continuous-type alarm. An event-type alarm has a timeout associated with it, while a continuous alarm is active as long as the alarm condition persists. The aSC 230a may then transmit its DEVICEStatus message including the combined results of all other local 20 controllers 290 and the service byte of the aSC 230a. The aSC 230a may then stop the demand corresponding to the service bit set to '0'. The demand may not be restarted until all devices restore the service bit and the resulting AND is equal to '1'. The demands from the 25 same demand group (e.g. heating) can be substituted. In an embodiment if a heat pump service is not available and the system requires heating, gas heating or auxiliary electric heating may be used instead. In such a case, 1)C ) C:1 17 ) 1 - 76 the aSC 230a may issue appropriate gas heating or electric heating demands. The service bits may be set in all DEVICEStatus messages in all possible device states. In an embodiment 5 of a routine VERIFICATION mode startup, the service bits are published by a particular local controller 290 on the RSbus 180 upon receipt by that local controller 290 of the first aSC_ChangeState message after reset. Alternatively, the service bits may be published upon 10 receipt by the publishing local controller 290 of an aSCAssignment message after an asynchronous device reset. The service bits may be continuously updated to match the state of the service as determined by the local controller 290. 15 FIG. 15 illustrates without limitation a method generally designated 1500 that is illustrative of a dialog between the aSC 230a and a demand unit 155, e.g., an Integrated Furnace Control (IFC) or an Air Handler Control (AHC). Command messages are represented by 20 underlined text. The method 1500 should not be considered a programming model or all-inclusive, but only as example to illustrate various principles of the disclosure. The method 1500 begins with a step 1510. In a step 1520 the aSC 230a determines if blower service is needed. 25 If yes, the method advances to a step 1530, in which the aSC 230a determines if blower service is available. If the blower service is available, the method advances to a step 1540. In the step 1540 the aSC 230a sends a BlowerDemand message to the IFC or AHC, as appropriate. 30 The method 1500 then advances to a step 1550. In the step 1550, the IFC or AHC transmits a DEVICEStatus message to the aSC 230a that includes the status of the blower. In a step 1560 the aSC 230a then sends a SC_UI_Zone_Status - 77 message to the UI 240 to provide feedback to the user/operator. If in the step 1530 the aSC 230a determines that blower service is not available, the method 1500 advances directly to the step 1550 without 5 issuing a BlowerDemand message. The method 1500 ends with a step 1570. Messages between any UI 240 and the aSC 230a may be sent as a Class 1 message. In various embodiments Class 1 messages have priority over other messages, thus 10 potentially reducing message latency. In most cases a display screen of the UI 240 is not updated with data directly from user input, but with data returned from the aSC 230a in response to the messages generated by the UI 240 in response to the user input. Exceptions to this 15 general rule include cases in which a user selection results in altered equipment operation, such as a mode change. In that case, the user input may be buffered at the UI 240 until the selection is finalized, which may be either explicit or by timeout. Once the user selection is 20 finalized, the UI 240 may send a message to the aSC 230a in response to the selection. Local controllers 290 may be configured to promptly reply to a demand message. In an example embodiment, the local controller 290 acknowledges receipt of the demand 25 message within about 100 ms by broadcasting a DEVICEStatus message. The DEVICEStatus message may have the Acknowledge bits set to Olb (ACK) if the message is positively acknowledged. Other aspects of the message may be otherwise unchanged from the case that no 30 acknowledgment is made. A 0% demand is typically acknowledged in the same manner as non-zero demands. For a staged demand unit 155, a demand below its minimum - 78 range may be treated as a 0% demand. In general, a demand message above 100% may be treated as a 100% demand. Turning now to FIG. 16, illustrated is a method of the disclosure generally designated 1600 of manufacturing 5 a subnet controller of an HVAC data processing and communication network. The method 1600 begins with an entry state 1610. In a step 1620, a bus interface device, e.g., the local controller 290, is configured to receive a message from a subnet controller over the network. The 10 subnet controller may be, e.g., the aSC 230a. In a step 1630, the bus interface device is configured to control a demand unit in response to the message. The method 1600 ends with an exit state 1640. FIG. 17 illustrates another method of the disclosure 15 generally designated 1700 of a method of manufacturing a bus interface device networkable in an HVAC data processing and communication network. The method 1700 begins with an entry state 1710. In a step 1720, a physical layer interface, e.g., the PLI 310, is 20 configured to interface to a data network, e.g., the RSBus 180. The physical layer interface may be located, e.g., on an active subnet controller such as the aSC 230a. In a step 1730 a communication module, e.g. the communication module 340, is configured to send and 25 receive messages over the data network via the physical layer interface. The communication module may be located, e.g., on a bus interface local controller 290. In a step 1740 a functional block, e.g., the functional block 350, is configured to reset in response to a message received 30 by the communication module. The functional block may be located on the same bus interface device as the communication module. The method 1700 ends with an exit state 1750. )C ')r1-72 11 - 79 FIG. 18 illustrates another method of the disclosure generally designated 1800 of a method of manufacturing a subnet controller of an HVAC data processing and communication network. The method 1800 begins with an 5 entry state 1810. In a step 1820, a physical layer interface, e.g., the PLI 310, is configured to electrically interface to the network. In a step 1830, a communication module, e.g., the communication module 340, is configured to send and receive messages over the 10 network via the physical layer interface. In a step 1840, a functional block, e.g., the functional block 350, is configured to respond to a message received by the communication module. The functional block thereby enters a disabled state in which the functional block does not 15 execute control functions, but the communication module may receive messages over the network. The method 1800 ends with an exit state 1850. FIG. 19 illustrates a method generally designated 1900 of manufacturing a device networkable in an HVAC 20 data processing and communication network. The method 1900 begins with an entry state 1910. In a step 1920, a physical layer interface is configured to interface to a network. The physical layer interface may be, e.g., the PLI 310. In a step 1930, a communication module, e.g. the 25 communication module 340, is configured to send and receive messages over the network via the physical layer interface. In a step 1940, a non-volatile memory is configured to store configuration data. The non-volatile memory may be, e.g., the NVM 320. In a step 1950, a 30 functional block, e.g., the functional block 350, is configured to respond to a message received by the communication module thereby enabling a privileged nr ff~ I - 80 operating mode not normally available to a user of the network. The method 1900 ends with an exit state 1960. FIG. 20 illustrates a method generally designated 2000 of manufacturing a device networkable in an HVAC 5 data processing and communication network. The method 2000 begins with an entry state 2010. In a step 2020, a physical layer interface is configured to interface to the network. The physical layer interface may be, e.g., the PLI 310. In a step 2030, a communication module, e.g. 10 the communication module 340, is configured to send and receive messages over the network via the physical layer interface. In a step 2040, a non-volatile memory, e.g., the NVM 320, is configured to store configuration data. In a step 2050, a plurality of logical devices is 15 configured to be addressable via the communication module. Each logical device is thereby capable of being independently disabled. The method 2000 ends with an exit state 2060. FIG. 21 illustrates a method of manufacturing a 20 device networkable in an HVAC data processing and communication network. The method 2100 begins with an entry state 2110. In a step 2120, a physical layer interface is configured to interface to a data network. The physical layer interface may be, e.g., the PLI 310. 25 In a step 2130, a communication module, e.g., the communication module 340, is configured to send and receive messages over the data network via the physical layer interface. In a step 2140, a non-volatile memory, e.g., the NVM 320, is configured to store device 30 configuration data. The messages include a first class of messages that address the device using only a Device Designator of the device, and a second class of messages that address the device using a message ID formed from a )C'IC1'7) *3 - 81 portion of the Device Designator and an offset. The method 2100 ends with an exit state 2150. FIG. 22 illustrates a method of manufacturing an HVAC data processing and communication network. The 5 method 2200 begins with an entry state 2210. In a step 2220, a first subnet controller, e.g., a first aSC 230a, is placed in communication with a first bus interface device over a data bus. The bus interface device may be, e.g., the local controller 290. In a step 2230, a second 10 subnet controller, e.g., a second aSC 230a or an iSC 230i, is configured to archive configuration data of the first subnet controller and the bus interface device. The method 2200 ends with an exit state 2240. FIG. 23 illustrates a method of manufacturing an 15 HVAC data processing and communication network. The method 2300 begins with an entry state 2310. In a step 2320, a demand unit is configured to provide a service having a maximum service capacity. In a step 2330, a subnet controller is configured to send a message to the 20 demand unit instructing the demand unit to provide a portion of the maximum. The method 2300 ends with an exit state 2340. FIG. 24 illustrates a method of manufacturing an HVAC data processing and communication network. The 25 method 2400 begins with an entry state 2410. In a step 2420, a first subnet controller and a second subnet controller are configured to communicate over the network. In a step 2430, the second subnet controller is configured to employ an arbitration algorithm to assert 30 control over the network and the first subnet controller. The method 2400 ends with an exit state 2440. Those skilled in the art to which this application relates will appreciate that other and further additions, n/nE1 7~ ') - - 82 deletions, substitutions and modifications may be made to the described embodiments. )If1C 11~7 1

Claims (8)

1. An HVAC data processing and communication network, comprising: a first system device adapted to provide a first service and publish a message including a first device status vector representing an availability of said first system device to provide said first service; and a subnet controller adapted to receive said message from said first system device including said first device status vector via a data bus; wherein said subnet controller is further adapted to receive, via messages from a plurality of system devices including said first system device, a corresponding plurality of device status vectors that includes said first device status vector, wherein each device status vector includes a plurality of bits, each bit having within said device status vector a bit position that corresponds to one of a plurality of potential services provided by said system devices, said plurality of services including said first service.

2. The network as recited in Claim 1, further comprising said plurality of second system devices.

3. The network as recited in Claim 1, wherein said subnet controller is adapted to determine an availability of said first service from said plurality of device status vectors.

4. The network as recited in Claim 1, wherein said subnet controller is adapted to perform a logical AND of a bit corresponding to said first service from each of said plurality of device status vectors to determine if said first service is available. 84

5. The network as recited in Claim 1, further comprising a user interface, wherein said subnet controller is adapted to generate a status message configured to display an alert on said user interface when said subnet controller determines from said first device status vector that said first service is unavailable.

6. The network as recited in Claim 1, wherein said first system device generates an alarm message in the event that said first service is unavailable.

7. A method of manufacturing a HVAC data processing and communication network, comprising: configuring a first system device to provide a first service and publish a message including a first device status vector representing an availability of said first system device to provide said first service; and configuring a subnet controller to receive said message from said first system device including said first device status vector, further configuring said subnet controller to receive, via messages from a plurality of system devices including said first system device, a corresponding plurality of device status vectors that includes said first device status vector, wherein each device status vector includes a plurality of bits, each bit having within said device status vector a bit position that corresponds to one of a plurality of potential services provided by said system devices, said plurality of services including said first service.

8. The method as recited in Claim 7, further comprising adapting said subnet controller to determine an availability of said first service from said plurality of device status vectors. 85 Lennox Industries Inc. Patent Attorneys for the Applicant SPRUSON & FERGUSON 10921803 1