JP2014174734A - Data communication system and master unit thereof, and data communication method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase reliability associated with data communication without changing an existing protocol.SOLUTION: The data communication system comprises: a master unit which issues a request signal for requesting data; and a slave unit which returns a response signal corresponding to the request signal, to the master unit. The master unit comprises a generation unit and a determination unit. The generation unit generates a request signal which includes information showing data and information showing a return code previously stored in the slave unit. The determination unit determines a correspondence between the request signal and the response signal. The slave unit returns the data shown by the request signal and the response signal which includes the return code. Then, the determination unit determines the correspondence between the request signal and the response signal on the basis of whether the return code requested by the request signal is included in the response signal.

Description

  Embodiments of the present invention relate to an improvement in a communication method for collecting data acquired by a sensor provided in, for example, a building or an industrial system.

  In a building such as a building, for example, various meters such as a meter for measuring the amount of water (flow rate of clean water), a meter for measuring the amount of heat related to air conditioning, or a watt hour meter are arranged. Sensing data once pooled in a PLC (programmable logic controller) or the like is collected by a higher-level host computer. PLCs are widely used to control industrial systems such as public systems such as water and sewage, factories such as steel and paper plants, buildings, public facilities, electric power receiving and transforming systems, central monitoring and control systems, and the automobile industry.

  The physical layer protocol in communication between the host computer and the PLC is typically a serial cable based on RS-485 or Ethernet (registered trademark). As an upper layer protocol, the Building Automation and Control Networking protocol (BACnet (registered trademark)) is famous, but the lower layer protocol is often a vendor's original specification.

JP 2004-70615 A

  Usually, a plurality of PLCs are connected to one host computer. In many cases, a method called single master / multi-slave is used as a data communication method between the host computer and the PLC in such a form. Under this method, the host computer (master) issues a request command (query), and the PLC (slave) returns a response. Since many lower layer protocols do not have means for associating a request with a response, the host computer determines the correspondence between the two based on the time series of the request and the response.

  However, when the response times out due to a communication failure or the like, the host computer issues the next request (command B). After that, when a response to the previous request (command A) arrives, the host computer regards this as a response to the command B and takes it as incorrect information. To make matters worse, all the correspondences between requests and responses in the subsequent data communication are shifted. In such a state, the reliability related to data communication is lost.

This kind of problem can be solved by implementing a sequence number in the protocol and associating the command with its response. However, it is practically difficult to implement a sequence number because it modifies an existing protocol that has already been established. There is a need for a technology that can solve the above problems without changing existing protocols.
It is an object of the present invention to provide a data communication system, a master unit thereof, and a data communication method with improved reliability without modifying existing protocols.

  According to the embodiment, the data communication system includes a master unit that issues a request signal for requesting data, and a slave unit that returns a response signal corresponding to the request signal to the master unit. The master unit includes a generation unit and a determination unit. The generation unit generates a request signal including information indicating data and information indicating a reply code stored in advance in the slave unit. The determination unit determines correspondence between the request signal and the response signal. The slave unit returns a response signal including the data indicated in the request signal and a reply code. Then, the determination unit determines the correspondence between the request signal and the response signal based on whether or not the reply code requested by the request signal is included in the response signal.

FIG. 1 is a system diagram showing an example of a building monitoring system to which the data communication system according to the embodiment can be applied. FIG. 2 is a functional block diagram showing the main part of the system shown in FIG. FIG. 3 is a functional block diagram illustrating an example of the PLCs 51 to 5N. FIG. 4 is a diagram showing an example of the relationship between the addresses of the data memories 5 of the PLCs 51 to 5N and the stored contents. FIG. 5 is a diagram illustrating an example of a format of data exchanged between the LCS 2m and the PLCs 51 to 5N. FIG. 6 is a functional block diagram illustrating an example of the LCS 2m in the embodiment. FIG. 7 is a diagram illustrating an example of the relationship between the address of the data memory 5 of the PLCs 51 to 5N and the stored contents in the first embodiment. FIG. 8 is a diagram illustrating an example of a format of data exchanged between the LCS 2m and the PLCs 51 to 5N in the first embodiment. FIG. 9 is a diagram illustrating an example of the relationship between the address of the data memory 5 of the PLCs 51 to 5N and the stored contents in the second embodiment. FIG. 10 is a diagram illustrating an example of a format of data exchanged between the LCS 2m and the PLCs 51 to 5N in the second embodiment.

  FIG. 1 is a system diagram showing an example of a building monitoring system to which the data communication system according to the embodiment can be applied. In FIG. 1, human interface stations (HIS) 11 to 1n, a global control server (GCS) 200, and local control servers (LCS) 21 to 2m are connected to a local area network (LAN) 100 in a building.

  A node is connected to each of the LCSs 21 to 2m via a communication line. Each node is, for example, an air conditioning device, a lighting device, or a power device for each floor. Each of the LCSs 21 to 2m recognizes a connected node as a monitored device, and monitors the state based on instruction values of various meters. The LCSs 21 to 2m store data based on the acquired signals for a certain period.

  The HISs 11 to 1n provide a graphical user interface (GUI) environment, and accept data input and setting changes by a user. Moreover, HIS11-1n acquires the count value of a meter, etc. from LCS21-2m, and preserve | saves the acquired data. Further, the HISs 11 to 1n receive data notified from the LCSs 21 to 2m and monitor and control the building monitoring system at a higher level and provide various information to the operator.

The GCS 200 periodically collects and accumulates meter value data in the building from the HISs 11 to 1n at a frequency of once a day, for example. Moreover, GCS200 controls the air conditioning, illumination, etc. of a building based on the various data acquired from LCS21-2m and HIS11-1n.
Furthermore, it is possible to connect the BEMS as the highest management system to the LAN 100 to optimize energy consumption and control comfort in the entire building.

  The LCSs 21 to 2m convert information to be transmitted into a communication format in BACnet (registered trademark) and transmit the information to the HISs 11 to 1n and the like. Since BACnet (registered trademark) is a standardized protocol, it becomes possible to connect different vendor systems to the LAN 100.

  In the embodiment, in FIG. 1, a plurality of PLCs 51 to 5N as slave units are connected to the LCS 2m as a master unit. Similarly to the above nodes, the PLCs 51 to 5N transmit the acquired data to the LCS 2m in response to a request. In the embodiment, consider data communication in the single master / multi-slave mode between the LCS 2m and the PLCs 51 to 5N. The LCS 2m functions as a host computer (master) for the PLCs 51 to 5N (slave).

  FIG. 2 is a functional block diagram showing the main part of the system shown in FIG. The PLCs 51 to 5N are cascade-connected via, for example, an RS-485 interface. The RS-485 interface is converted into, for example, Ethernet (registered trademark) by the protocol converter 40 and connected to the LCS 2m. The LCS 2m collects data from the PLCs 51 to 5N by a single master method.

  FIG. 3 is a functional block diagram illustrating an example of the PLCs 51 to 5N. In FIG. 3, a main CPU (Central Processing Unit) 1 is a central part of PLCs 51 to 5N that is responsible for execution and control of a sequence. The program memory 2 is a memory for storing a sequence program executed by the CPU 1, and stores an OS (Operating System), a sequence program interpretation program, an execution program, and the like.

  The work memory 3 is used as a work area when the CPU 1 executes a program. The sequence program memory (user program memory) 4 stores a sequence program. The data memory 5 stores various data required for operation of the building monitoring system, such as data acquired by the PLCs 51 to 5N from sensors (not shown) or data calculated by the PLCs 51 to 5N themselves. This type of data includes healthy counters, digital signals (such as on / off signals), analog signals (such as temperature and humidity sensing values), and integrated value signals (such as electric power and refrigerant flow rate integrated values). is there.

  The microcomputer bus 6 is a bus for connecting the elements in the PLC to the CPU 1 and is an entire address bus, data bus, and control bus. An I / O (Input / Output) 7 is an input / output device for connecting a PLC and an external control target (such as a sensor). A communication interface (communication I / F) 8 is an interface for connecting PLC and LCS via a communication line. The trace CPU 9 is connected to the CPU 1 and various memories via the microcomputer bus 6 and assists the autonomous operation of the PLC while monitoring signals on the microcomputer bus 6.

  FIG. 4 is a diagram showing an example of the relationship between the addresses of the data memories 5 of the PLCs 51 to 5N and the stored contents. Address (D0000) is a healthy counter value, addresses (D0001) to (D00110) are digital signal values, addresses (D0011) to (D0100) are analog signal values, and addresses (D0101) to (D0200) Each stores the value of the integrated value signal.

  In the existing protocol, for example, the area after the address (D0201) is set as a free area. In the embodiment, the specific information is stored in a specific address (for example, (D1000) or later) in this area.

FIG. 5 is a diagram illustrating an example of a format of data exchanged between the LCS 2m and the PLCs 51 to 5N. The format of the request signal issued from the LCS 2m to the PLCs 51 to 5N is as follows: the PLC number (03) following the header (A), the command type, the read address, the comma (,), the number of request signals, the & symbol, and the checksum. Arranged. In FIG. 5, (DR) is designated as the data read command. The request signal shown in FIG. 5 is a command for requesting 30 (word) data from the read address (D0041).
In response to this request signal, the response signal returned from the PLC designated as (03) includes the PLC number (03) following the header (A), the command type, reply data 1 for the requested number, and the requested number. Reply data 2, & symbol and checksum are arranged in this order.

FIG. 5 shows an example in which data in a plurality of memory areas can be acquired with one request signal. The description of (read address 1) in the request signal shown in FIG. 5 suggests that (read address 2), (read address 3),... Can also be specified. That is, it is possible to describe a plurality of start addresses of data to be acquired in the request signal.
In the response signal shown in FIG. 5, the description of reply data 1 and reply data 2 indicates that data read from two different memory areas is included in one response message.

  Since the message format shown in FIG. 4 and FIG. 5 does not include a sequence number (serial number or the like) for distinguishing signals, there is a case where data transfer is not completed correctly due to a timeout after issuing a request signal. In addition, when a plurality of response signals are copied and arrived due to network problems (such as congestion or re-transmission processing by PLC), the correspondence between the request signal and the response signal breaks down, and the LCS contains incorrect data. Will be taken in. In the following, a technique capable of solving this type of problem without modifying an existing protocol is disclosed.

[First Embodiment]
FIG. 6 is a functional block diagram illustrating an example of the LCS 2m in the embodiment. The LCS 2m includes a communication interface 30, a storage unit 31, and a control unit 32. The communication interface 30 has a communication interface function with the PLCs 51 to 5N and the LAN. The control unit 32 realizes various processing functions of the LCS 2m based on a program stored in the storage unit 31.

  The control unit 32 includes a writing unit 32a, a generation unit 32b, and a determination unit 32c as processing functions according to the embodiment. Of these, the writing unit 32a writes the reply code in a predetermined storage area of the data memory 5 provided in the PLCs 51 to 5N.

  FIG. 7 is a diagram illustrating an example of the relationship between the address of the data memory 5 of the PLCs 51 to 5N and the stored contents in the first embodiment. In FIG. 7, the same contents as in FIG. 4 are stored from address (D0000) to (D0200), but various reply codes are written after address (D1000) in address (D0201) which is an empty area. . The plurality of reply codes are written by the LCS 2m when the LCS 2m is activated or when the LCS 2m detects a return from the abnormality of the PLCs 51 to 5N.

  The reply code is data defined for each request command, and is a unique value that can be uniquely identified. In FIG. 7, the reply code can be distinguished by describing the head address of each request command. For example, for a command requesting the value of a PLC healthy counter, the address (0000) where the value of the healthy counter is stored is used as a reply code.

  In particular, in a protocol that can exchange data up to a limited number of words (for example, 31 words) in one response, it is necessary to divide the data into a plurality of times and exchange it. In order to support such a protocol, as shown in FIG. 7, a number of reply codes corresponding to the number divided for each data are prepared and stored. For example, the return codes (0011), (0041), and (0071) are stored for each of the first, second, and third divided data so that the analog signal can be transferred in three times. These reply codes are the top addresses of the respective data. Similarly, the integrated value signal can be transmitted and received divided into four times.

  Returning to FIG. 6, the generation unit 32 b generates a request signal for reading desired data from the data memory 5. The request signal includes information indicating data to be acquired and information indicating a return code. Among these, the information indicating the data to be acquired is, for example, the read address of the data and the number of words as shown in FIG. The information indicating the reply code is the reply code address and the number of words.

  The determination unit 32c determines the correspondence between the request signal generated by the generation unit 32b and issued to the PLC, and the response signal returned from the PLC in response to the request signal. Specifically, the determination unit 32c determines the correspondence between the request signal and the response signal based on whether or not the reply code requested by the issued request signal is included in the returned response signal.

  FIG. 8 is a diagram illustrating an example of a format of data exchanged between the LCS 2m and the PLCs 51 to 5N in the first embodiment. The difference from the format of FIG. 5 is that information requesting a return code is described following the data read command (DR).

  In the request signal shown in FIG. 8, following the command DR, the address (D1003) of the second reply code of the analog signal and the word number 01 of the reply code with a comma (,) are described. With this information, one word of information described in the address (D1003), that is, a reply code (0041) is requested.

  Upon receiving this request signal, the PLC writes (0041) in the response signal (reply data 1) and returns it to the LCS 2m. By verifying the correspondence between the return codes, the LCS 2m can determine the correspondence between the issued request signal and the received response signal.

  As described above, in the first embodiment, when the master unit reads data to the slave unit a plurality of times, the address of the data in the target range and the address where the corresponding return code is stored are specified. Issue a read command. Then, the master unit determines that the received response is data in the target range based on the reply code.

  That is, the LCS 2m specifies the address of the corresponding reply code in addition to the address of the area where the target data is stored in the request signal for requesting data acquisition. The PLC that has received the request signal returns a response signal including data (return code and target data) of the requested address.

  When the LCS 2m receives the response signal, the LCS 2m compares the first word (response code) of the response signal with the response code corresponding to the target data, and accepts the response signal if both are the same. If they are not the same, it is determined that the response signal is not a response corresponding to the request, the response signal is discarded, and the next response signal is awaited.

  In the above procedure, the format of the request signal and the response signal is not different from the existing protocol. That is, according to the first embodiment, information for associating a request signal with a response signal can be exchanged between the LCS and the PLC without changing the existing protocol. Therefore, it is possible to provide a data communication system, a master unit thereof, and a data communication method with improved reliability without modifying existing protocols.

[Second Embodiment]
FIG. 9 is a diagram illustrating an example of the relationship between the address of the data memory 5 of the PLCs 51 to 5N and the stored contents in the second embodiment. In FIG. 9, each data area and a reply code corresponding to the data area are arranged successively. That is, the reply code and the target data are arranged as data in a single memory range. According to such data arrangement, it is possible to request both the return code and the target data by one data request command (request signal).

  FIG. 10 is a diagram illustrating an example of a format of data exchanged between the LCS 2m and the PLCs 51 to 5N in the second embodiment. The request signal includes the address where the reply code is stored and the number of words (31) that is the sum of the reply code and the target data. Upon receiving this, the PLC returns a response signal including the reply code at the head of the reply data string and the remaining 30 words including the target data.

  In the first embodiment, as shown in the format of FIG. 8, it is possible to request data in a plurality of storage areas with one request signal. However, there is a protocol that can request only data in a single storage area with one request signal. According to the second embodiment, it is possible to cope with such a protocol.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

  DESCRIPTION OF SYMBOLS 11-1n ... Human interface station (HIS), 200 ... Global control server (GCS), 21-2m ... Local control server (LCS), 100 ... LAN, 40 ... Protocol converter, 1 ... Main CPU, 2 ... Program memory 3 ... work memory, 4 ... sequence program memory, 5 ... data memory, 6 ... microcomputer bus, 7 ... I / O, 8 ... communication interface, 9 ... trace CPU, 30 ... communication interface, 31 ... storage unit, 32 ... Control unit, 32a ... writing unit, 32b ... generating unit, 32c ... determining unit

Claims (9)

A master unit that issues a request signal for requesting data;
A slave unit that returns a response signal corresponding to the request signal to the master unit;
The master unit is
A generating unit that generates the request signal including information indicating the data and information indicating a reply code stored in advance in the slave unit;
A determination unit for determining correspondence between the request signal and the response signal;
The slave unit returns a response signal including data and a reply code indicated in the request signal,
The data communication system, wherein the determination unit determines a correspondence between the request signal and the response signal based on whether or not a reply code requested by the request signal is included in the response signal. The slave unit includes a memory for storing the data in a storage area,
The data communication system according to claim 1, wherein the master unit includes a writing unit that writes the return code in a predetermined storage area of the memory.   The data communication system according to claim 2, wherein the information indicating the reply code is an address and the number of words of the reply code stored in the memory. In the master unit that issues a request signal for requesting data to the slave unit,
A generating unit that generates the request signal including information indicating the data and information indicating a reply code stored in advance in the slave unit;
Determination that determines the correspondence between the request signal and a response signal returned from the slave unit in response to the request signal based on whether the response signal includes a response code requested by the request signal And a master unit.   The master unit according to claim 4, further comprising a writing unit that writes the return code in a predetermined storage area of a memory provided in the slave unit.   The master unit according to claim 5, wherein the information requesting the reply code is an address and the number of words of the reply code stored in the memory. In a data communication method between a master unit that issues a request signal for requesting data and a slave unit that returns a response signal corresponding to the request signal to the master unit,
The master unit generates the request signal including information indicating the data and information indicating a reply code stored in advance in the slave unit;
The slave unit returns a response signal including data and a reply code indicated in the request signal,
A data communication method, wherein the master unit determines correspondence between the request signal and the response signal based on whether or not a reply code requested by the request signal is included in the response signal.   The data communication method according to claim 7, wherein the master unit writes the reply code in a predetermined storage area of a memory provided in the slave unit.   The data communication method according to claim 8, wherein the information indicating the reply code is an address and the number of words of the reply code stored in the memory.

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