GB2229560A - A status and control multiplex communications system - Google Patents

Abstract

Status and control information is exchanged between at least one remote site A1-3 and a control point C. A multiplexer (SMUX) at each remote site A operates to scan the remote site status points to be monitored to generate one equivalent voice bandwidth transmission channel which services a large number of status/control circuits. The multiplexer (SMUX) at each remote site comprises a hardware universal asynchronous receiver transmitter (UART) chip (SMOX). This chip accepts, for example, 8 parallel input bits and produces a continuous string of serial ASCII format output signals for transmission to a control point. The multiplexer utilizes at least one TTL 16-to-1 multiplex chip, whose inputs are sequentially scanned by 4 address lines, and whose data output is connected to one of the parallel data inputs of the UART. These address lines are also connected to 4 other parallel data inputs of the UART. The UART transmits a serial ASCII format character for each sequential address of the 16-to-1 multiplex chip. Each character contains the address of the 16- to-1 multiplex input line being scanned and the corresponding data in 5 of the available 8 data bits. 16 sequential serial ASCII characters constitute one complete scan of all status/control input lines. <IMAGE>

Description

STATUS AND CONTROL MULTIPLEX SYSTEM This invention generally relates to radio frequency (RF), telephone cable, fiber optic and other communications systems having a control site and at least one remote site.

In many communications systems, there is an ever increasing need for status reporting and the exercise of various control functions between a control site and at least one remote fixed site.

For example, in a multiple site RF transmission system employing simulcasting, a simulcast remote site typically has a large number of status points (e.g., forward and reflected. power monitors, smoke alarms, etc.) for which it would be desirable for a control site to periodically monitor.

Such simulcast systems, which typically provide RF communications to a large geographical area such as a major metropolitan area, large county, etc., often include multiple RF repeater transmission sites each having a large number of status points.

It is typically not possible for a single VHF/UHF RE repeater transmitting site to satisfactorily serve an arbitrarily large geographical coverage area.

Legal and practical maximum effective radiated power limitations and natural topographical features block signal transmission in certain areas or prevent a transmitting antenna from being installed at sufficient elevations.

Referring by way of background to figure 1, there is shown a general block diagram of an exemplary (ie illustrative) multiple-site system having three radio repeater (transmitting) sites Sl, S2 and S3 providing communications to geographical areas Al, A2 and A3, respectively. A control point or "hub" C in the exemplary simulcast system provides identical signals to each of sites Sl-S3 via links L1-L3, respectively. These links are typically microwave links but may be landline or other type links. Each of the repeater staticns S1, S2, and S3 may, for example, include 10 or more base station transmitters, and associated data transmitting equipment, high stability oscillators and other equipment necessary for forming a simulcast remote site.Each site S1-S3 transmits the signals it receives from the control point C to its respective coverage area Al-A3 so that a mobile or portable transceiver receives the same signal no matter where it happens to be in the communication systems overall coverage area.

There is a need to determine that the remote sites S1-S3 and the control point C are operating correctly. It is also desirable to be able to monitor the status of the remote sites and to control predetermined functions at the remote sites to reduce the need for periodic inspection and maintenance visits to these sites. Thus, it is desirable for control point C to be remotely informed of a malfunction or condition requiring action such as: the transmitter is not broadcasting properly; a high stability oscillator is not operating properly, or the site has been broken into.

The need for remotely monitoring and controlling remote status points becomes most critical where, for example, control point C is located in a central metropolitan area and stations S1, S2 and S3 are each located on relatively inaccessible mountaintops many miles from the control point C.

Aspects of the present invention are set out in the claims to which attention is directed. Other aspects may be apparent from the following description.

In an illustrative (exemplary) embodiment of one aspect of the present invention, in order to efficiently satisfy the need for remote monitoring and control, sensors are associated with various key monitoring points at one or more of the remote sites. GO/NO-GO logic signals are generated by each of these sensors either by way of input contact closures or predetermined sensed voltage levels.

Multiplexing circuitry (which itself forms an embodiment of another aspect of the present invention) at each remote site operates to scan the remote site status signals being monitored to generate one equivalent voice bandwidth transmission channel which services up to, for example, 64 status/control circuits. The equivalent voice bandwidth channel can either be an asynchronous data channel, such as might be found in a standard telephone "T" carrier system or an analog multiplex channel with appropriate data modems.

In either case, in accordance with the exemplary (ie illustrative) embodiment, the data channel handles asynchronous ASCII format data at a rate consistent with the desired throughput time for the status/control circuits.

Links Ll-L3 shown in Figure 1 may each consist of, by way of example, 48 full duplex voice/data grade channels.

One of the 48 channels in each link is dedicated to providing status and alarm information from a remote site S1-S3 back to the control point C and to provide remote control capability to control point C. In accordance with the exemplary embodiment, the disclosed multiplexer system allows up to 64 status and control circuits to be served via one equivalent voice bandwidth channel.

Preferably, the digital status and control multiplex system at each remote site in the exemplary embodiment comprises a hardware universal asynchronous receiver transmitter (UART) chip. This chip is configured to accept 8 parallel input bits and produce a continuous string of serial ASCII format output signals. The multiplexer system utilizes at least one TTL 16-to-l multiplex chip, whose inputs are sequentially scanned by 4 address lines, and whose data output is connected to one of the parallel data inputs of the UART. These address lines are also connected to 4 other parallel data inputs of the UART. The UART transmits a serial ASCII format character for each sequential address of the 16-to-l multiplex chip.Each character contains the address of the 16-to-l multiplex input line being scanned and the corresponding data in 5 of the available 8 data bits. 16 sequential serial ASCII characters constitute one complete scan of all status/control input lines. Scanning of the status/control inputs is continuous. Hence, there is a continuous stream of serial data and each status/control line is continuously updated.

It is noted that, in addition to simulcast systems, any communications system having a control site where there is a large number of users would benefit from the multiplexing features of the present invention. For example, a communications system having a site controller which controls on the order of 25 to 50 base stations, or is otherwise utilized by a great number of users, would benefit from the remote status sensing and control features of the present invention, particularly where the controlled sites are remotely located.

The present invention will be better appreciated by reading the following detailed description of a presently preferred exemplary (ie illustrative) embodiment of the present invention taken in conjunction with the accompanying drawings of which: FIGURE 1 is block diagram of a simplified multiple-site system having three radio repeater (transmitting) sites S1, S2 and S3 providing communications to geographical areas Al, A2 and A3, respectively; FIGURE 2 is a block diagram of one of the multiplexer units shown in Figure 1 while implementing an encode function in accordance with an exemplary embodiment of the present invention; FIGURE 3 is a block diagram of one of the multiplexer units shown in Figure 1 while implementing a decode function in accordance with an exemplary embodiment of the present invention;; FIGURE 4 is a more detailed schematic diagram of the multiplexer units shown in Figures 2 and 3; and FIGURE S is a block diagram of an exemplary alarm unit which may be used in conjunction with the status and control multiplexer system of the present invention.

Turning back to the multi-site status and control multiplex communications system shown generally in Figure 1, by way of example only, it will be presumed that each radio repeater site S1, 52 and 53 is a 10-channel site. Each remote site has a large number of status points SP1-SPN which are monitored, and reported to control point C.

Additionally, each remote site may be remotely controlled via control signals received from control point C.

Multiplexer units SlMUX-53MUX and CMUXl-CMUX3 (which are described in detail in Figures 2-4) are shown generally in Figure 1. These units may be identical and are, in the exemplary embodiment, implemented by printed circuit cards and are utilized at both the repeater base stations 51-53 (i.e., SlMUX-S3MUX) and at the control point C (i.e., CMUXl-CMUX3) to provide channels carrying status information from the radio base repeatcrs to the control point C and control information from control point C to the repeater base stations. In the present exemplary embodiment, the control point C has three multiplexer units (i.e., CMUXl-CMUX3).

Each multiplexer unit is coupled to a set of associated control switches and an alarm unit (i.e., Control SW and Alarm Units 1-3). Actuation of one of the control switches results in the generation of coded signals identifying one of the control functions to be described below. Exemplary alarm units 1-3 are described in detail in conjunction with Figure 5.

At each exemplary 10-channel remote site 51-53, individual sensors are associated with each of the status points being monitored. Each of the sensors may be conventional, commercially available sensors which, for example, indicates å change of status by generating a signal upon the closure of a relay contact. For a detailed disclosure of exemplary sensors of the type used to monitor remote site status points, reference is made to commonly assigned copending application 07/085,663, filed August 14, 1987 and entitled "Radio Trunking Fault Detection System", which application is hereby expressly incorporated herein by reference.

By way of example only, 10 individual forward power monitors are utilized at each remote site S1-S3 to provide an indication that each of the 10 transmitters is on the air and therefore is producing a power output. Additionally, each remote site S1-S3 includes 10 individual reflected power monitors which indicate if any of the RE signal power to be transmitted is being reflected back to the transmitter down the RF transmission line. The individual reflected power monitors also provide a mechanism for determining whether the transmitter combiner at each remote site 51-53 (which combines the 10 transmitters into a common antenna) is functioning properly.

The monitoring system at each remote site S1-S3 also includes an antenna forward power monitor and an antenna reflected power monitor to monitor the output of the transmitter combiner. Additionally, major and minor alarm status conditions associated with the multiplexers at the repeater stations S1-S3 are monitored as are alarm conditions associated with the microwave links at each of the remote sites. These multiplexer and microwave link alarm status conditions are triggered by relay closures and are reported back to the control point C via the multiplexing units SlMUX-S3MUX. It is noted that the multiplexer and the microwave system alarms are conventionally provided by the associated multiplex and microwave equipment manufacturers.

Additionally, the status of alarms associated with repeater station building entry, building temperature, smoke detectors, thermostats, etc., can be monitored. By monitoring the building entry alarm, it can be remotely determined whether an unauthorized- party has entered the building containing the radio repeater base station.

Additionally, it can be determined whether an authorized party has entered the building within a predetermined period of time, e.g., to service or repair equipment.

The system also monitors the alarms associated with the computer serving as the site controller at a remote station 51-53. Such a site controller is disclosed, for example, in U.S. Patent 4,682,367, which patent is hereby incorporated by reference.

Additionally, the present system monitors the status of, for example, 10 alarms associated with each of the receivers at the remote sites 51-53. In this regard, the receiver output signal, DC current consumed, noise level, etc., may be monitored.

The status points of the remote sites S1-53 described above as being monitored are exemplary only. Preferably the system contemplates monitoring as many remote site conditions as possible so that the status information returned to the control point C is sufficient to allow an operator to diagnose any problem at the remote site and determine what portions of the repeater system need to be repaired or replaced. By providing 64 status points which may be monitored via the multiplexing units shown in Figures 2 through 4, the present system provides sufficient status information to the control point C to permit an accurate fault analysis to be made.

As will be described further below, each of the exemplary multiplexing units shown in Figures 2 through 4 transmits the status/control information by accepting up to 64 TTL level inputs in 4 blocks of 16 and converting them into a composite string of serial 10-bit characters in an ASCII format (i.e., a leading zero, eight data bits and a trailing one).

A total of 16 sequential ASCII characters constitutes a complete scan of the radio repeater status points. At the control point C, the received characters are decoded by the appropriate multiplexer unit CMUX1-CMUX3, analyzed and utilized to drive display devices to reflect the status of each radio repeater base station S1-S3 and to indicate any fault condition which requires servicing.

Since the generated characters are in ASCII format, the data is computer readable. Thus, the received data may be input to a serial input port of a digital computer located, for example, at control point C. The computer may then analyze the received data to determine whether a fault condition exists.

By analyzing the 8 data bits associated with an ASCII character, it can be readily determined which of the status points of a particular radio repeater base station is being sensed as well as the status condition indicated by the data. As will be explained further below, status point identifying data is inherently transmitted as a part of the ASCII characters. In this regard, the present system is self-synchronizing since the channel or sensor identifying information is inherent in the data format.

In addition to the 64 status points that may be reported from radio repeating stations S1-S3, 64 control functions may be triggered by the actuation of control switches at control point C to generate control signals to be transmitted to the remote site radio repeater stations S1-S3. In regard to the outbound control functions utilized in the exemplary embodiment of the present invention, the system incorporates channel reset lines which may be used to reset the site controllers at the radio repeater base stations S1-S3. Thus, if a site controller associated with one of the radio repeater stations is not operating properly, control point C can remotely reset the site controller.

In regard to the 10 transmitters at a 10 channel remote site (e.g., site S1), one or more of the transmitters may be placed in a test mode by generating a transmitter test initiate signal at control point C. Additionally, any one or more of the transmitters may be inhibited under the control of the control point C. In this fashion, any transmitter may be disabled if it is not operating properly.

The system additionally implements an interrogate site fault sensing equipment control function. In this regard, not only can the system interrogate the critical status points relating to building entry, temperature and smoke alarms, but it can also trigger the operation of, for example, a scanning device at a remote site which scans any other additional sensors to indicate whether, for example, tower lights are operating properly. The system additionally includes (for a 10 channel remote site) 10 data loop-back test initiate control functions and 10 audio loop-back test initiate control functions. In this fashion, the control point C can test the data modems or the audio circuitry by individually looping back both audio and data to test the operability of the data and audio paths as an aid in diagnosing errors in the system.

The status/ control multiplexing units of the system shown generally in Figure 1 are shown in detail in Figures 2 through 4. Figures 2 through 4 show the structural details of the identical multiplexer units SlMUX-S3MUX, and CMUX1- CMUX3 disposed at the remote sites S1-S3 and at the control point C, respectively. Each of the multiplexing units operate over a full-duplex asynchronous ASCII data channel to provide both encode and decode modes.

However, the two directions of information data flow are totally independent. Figure 2 shows the multiplexer unit block diagram configuration while implementing the encode function and Figure 3 shows the unit configuration while implementing the decode function.

In accordance with a preferred embodiment of the present invention, rather than providing a separate voice grade or wire line circuit for each inbound status information or outbound control function, only one equivalent voice bandwidth transmission channel is used for up to 64 status/control circuits. Since microsecond response times are not critical for most status and control circuits, the multiplexing techniques implemented by the multiplexing apparatus shown in Figures 2 through 4 economically provide a large number of status/control channels over a single transmission channel.

The status/control multiplexer system of the present system accepts at each of the remote sites S1-S3 and the control point C up to 64 TTL level inputs in 4 blocks of 16 and converts them to a string of serial 10bit data words in an ASCII format (i.e., a leading 0, 8 data bits and a trailing one).

The multiplexer system operating in the encode mode may minimally include, as shown in Figure 2, a multiplexer 2, which is coupled to a universal asynchronous receiver transmitter (UART) 10 and a clock/counter/control logic 12, which is coupled to both the multiplexer 2 and the UART 10. This minimal system is capable of receiving a 16 input block defining the state of 16 remote site status points for transmission to the control point C. As will be explained further below, by adding the 3 additional multiplexer units 4, 6, and 8, the system may be readily expanded from 16 to 64 status/control channels without increasing system throughput time.

Figure 2 shows the system configuration for expanded operation by depicting the additional multiplexers, 4, 6, and 8 and the associated component interconnections with dashed lines.

Multiplexers 2, 4, 6, and 8 are each single integrated circuit TTL 16-to-1 multiplexer chips.

Each multiplexer chip may, for example, be an industry standard TTL device type 74150. Each multiplexer chip is a scanned device having 16 inputs (identified as blocks 1, 2, 3, or 4). Each multiplexer 2, 4, 6, and 8 has coupled thereto 4 address lines which receive a 4-bit address for each of the multiplexers. For example, the four address lines associated with multiplexer 2 are identified as G in Figure 2.

Each of the multiplexers additionally has a data output which is coupled to UART 10. For example, the output of multiplexer 2 is identified in Figure 2 as H. The data transmitted on a multiplexer output line (e.g., H) is the data present on the particular on of the 16 data input lines that is uniquely identified by the 4-bit address appearing on address lines G. The same 4 bit address is simultaneously coupled to each multiplexer 2, 4, 6, and 8 from address control logic 12.

The data inputs of each multiplexer are sequentially scanned by the four address lines and the data output of each multiplexer is connected to one of the parallel data inputs of UART 10. Each multiplexer output provides one data bit of the ASCII data train comprising the serially transmitted ASCII output character.

The UART 10 may, for example, be a Western Digital UART, type 1863. This chip accepts 8 parallel input bits and produces a serial data ASCII format output signal (K).

The UART 10 transmits a serial ASCII format character for each sequential address of the 16 to 1 multiplexer chips 2, 4, 6, and 8.

Each outputted ASCII character contains the address of the 16 to 1 multiplexer input line being scanned and the corresponding data in 5 of the available 8 data bits.

Sixteen sequential serial ASCII characters constitute one complete scan of all status/control input lines. Scanning of the status/control inputs is continuous. Hence, there is a continuous stream of serial data at the UART output K which is being continuously updated.

The data and scanning rates are determined by the clock/counter/control (control logic) 12. Thus, the control logic 12 generates the four binary address bits to drive the scanning of each of the multiplexers 2, 4, 6, and 8. As shown in Figure 2, the 4 address bits on lines G are also transmitted as 4 data bits via UART 10.

Thus, the 4 address bits serve to select the multiplexer input line for transmission as multiplexer output data. Additionally, address bits are transmitted as data to the remote sites S1-S3.

In this fashion, system synchronization is automatically achieved since the address data transmitted via lines G identify which of the 16 input lines of a particular multiplexer is being scanned and the data on line H identifies the status of that input line.

Advantageously; the same address data is utilized for each of the additional multiplexers 4, 6, and 8 as shown in Figure 2. For each additional multiplexer module which is added to the system, only one additional data line need be added. The one additional data line associated with each of multiplexers 4, 6, and 8 is shown in Figure 2 lines El, E2 and E3, respectively. Thus, of the 8 input bits transmitted in parallel to UART 10, bits T1-T4 represent the address that is being scanned and bits T5-T8 represent the status of the identified input line of multiplexer 2, 4, 6, and 8, respectively.

The design of a minimal system shown in Figure 2 (i.e., a unit having one multiplexer chip 2) allows for system expansion by adding 16 input blocks without changing response time. System expansion is accomplished by adding additional 16 to 1 multiplexer chips, e.g., 4, 6, and 8. As noted above, address lines G are connected to each of the multiplexer chips. The data outputs (e.g., El, E2 and E3) of the added multiplexer chips 4, 6, and 8 are connected to the 3 remaining parallel input bits (T6, T7, T8) of UART 10. This results in all of the multiplexer chips 2, 4, 6, 8 being scanned in parallel. Since parallel data paths H and El, E2, and E3 are provided for each 16 input data block, no increase in throughput time results when expanding from 16 to 64 status/control channels.Furthermore, it is not necessary to have the same number of 16 status/control channel blocks operating in both directions between a remote site S1-S3 and the control point C.

Focusing on the operation of Figure 2, a crystal oscillator within control logic 12 is utilized to generate the required clock frequency to drive the UART 10 while also producing the scanning frequencies transmitted to multiplexers 2, 4, 6, and 8 (via address lines G). The signals generated by control logic 12 are a sequence of square waves.

Depending upon the address defined by the signals on the address lines G, a predetermined one of the sixteen inputs of each multiplexer is selected as the data output and applied to lines H, El-E3, respectively. These output signals are delivered to the UART 10.

The address signal applied to the multiplexers 2, 4, 6, and 8 is incremented such that all inputs are scanned repeatedly. Thus, the address defined by control logic 12 is incremented, after which an input from each of the multiplexers is scanned in parallel, the UART 10 is caused to send the input data as a single ASCII data word, after which the address is again incremented to define a further scanning operation. During this process the control logic 12 allows time for the signals on address lines G to stabilize. After the output data is selected and given time to stabilize the data is transmitted in ASCII format.

The serial data output from Figure 2 (K) in order to be properly decoded by the hardware shown in Figure 3 must be in a predetermined format such as the ASCII format described above. The data may be transmitted, for example, via a microwave link, telephone lines via data modems, over a radio channel or any other voice grade communication medium.

Turning to Figure 3, receiving of transmitted serial data is accomplished in the reverse manner of that described with respect to Figure 2. In this regard, the repetitive string of serial ASCII format data signals (L) is connected to serial receiver input of UART 10. Eight parallel data bits on lines X, N, and W are delivered to the appropriate output latches 16, 18, 20, and 22 along with the strobe pulse U which indicates that a new serial data word has been received. In the exemplary system, the latches are industry standard TTL devices type 74us259.

The four received address bits (R1-R4) on lines N select the proper addressable latch output. The data on line M contained in the fifth parallel data bit is latched in the selected output of the addressable latch 16. Each successive serial data character accesses the next sequential latched output which exactly tracks the selected input as transmitted so that data synchronization is automatic.

System expansion at the receiving end beyond the UART 10, control logic 14, and a single output latch 16 is indicated by the components and interconnections shown in dashed lines. As shown in Figure 3, such expansion only requires the incorporating addressable output latches 18, 20, and 22 to thereby add three blocks of 16 channels. The address signals on lines N and the strobe signal on line U are bussed to all four output latches. The data inputs on line W of blocks 2, 3, and 4 are connected respectively to the remaining three parallel output bits (R6-R8) of UART 10. This results in the four blocks of 16 lines being scanned in parallel thereby resulting in no additional throughput time as channel capacity is increased.

Additionally, the received data bits 1-4 which appear in Figure 3 on line N identify the address of the addressable latch output. The data defined by received bits 5-8 are then latched into the selected output of the appropriate output latch 16, 18, 20, and 22. In this fashion 64 outputs are generated in four blocks of 16 bits as shown in Figure 3.

The received serial data L is as noted above in standard ASCII format and is therefore machine readable. Accordingly, the decoding function shown and implemented in hardware in Figure 3 may alternatively be decoded under software control by being delivered directly to an ASCII serial input of a computer disposed at either the control point C or repeater base station S1-S3.

By transmitting the scanning or address information along with the data, synchronization problems are avoided since the system automatically knows by virtue of the received address information, the channel in each of the four blocks which is being scanned. Thus, if channel 1 of block one is being scanned, as indicated by decoding of the address information on lines N, then the system likewise knows that channels 17, 33, and 49 of blocks 2, 3, and 4, respectively, are being likewise scanned. Sixteen consecutive ASCII words are transmitted so as to scan all the channels in each of the blocks.

Focussing on the operation of Figure 3, serial data in ASCII format is received and converted by a conventional level converter to TTL signals and delivered to a serial input of UART 10. Upon receipt of the data, timing signals are generated and transmitted to control logic 14. The control logic 14, upon receiving an indication that the UART 10 has received data in the proper format, triggers the UART 10 to deliver the address data on lines N to output latches 16, 18, 20 and 22, which serve to demultiplex or decode the received data.

Each output latch receives data on a data line (e.g., M shown with respect to latch 16) and steers the received data to one of 8 predetermined outputs. It is noted that in order to obtain the 16 TTL alarm outputs, 2 latches are actually utilized together to form one of the output latches 16, 18, 20 and 22 as will be described below with respect to Figure 4. One of the bits in the address on lines N defines which of the two latches, comprising for example, output latch 16, is to receive the data.

The address on lines N also defines which of the outputs the data on line M will be steered to.

The control logic 14 serves to inform the system when the received serial data in the UART 10 is stable. The control logic responds to signals from the UART indicating that a new data word has been received. The control logic also serves to strobe the data into the output latches via signals transmitted on strobe line U. Additionally, the control logic resets a receive register in the UART 10 to indicate that another data word may be received. Thus, the control logic 14 serves to provide word synchronization to the multiplexer unit operating in a receive mode.

The multiplexer system as implemented by the circuitry to be described below in conjunction with Figure 4, accepts a serial 10 bit ASCII format signal input from, for example, another status/control multiplexer system and delivers up to 64 latched TTL level output signals. The maximum response or throughput time for an input to the corresponding output is approximately 256 times 1 bit time. The average throughput time is 1/2 the maximum time or 128 times 1 bit time.

The maximum response time is thus determined by presuming for a given data rate that the status of a particular status point changes immediately after a scanning operation. The following table identifies how long it will take before that input is scanned again. The maximum throughput in the table indicates how long it will take the exemplary circuitry in Figure 4 to transmit all 16 frames.

BAUD BIT TIME . MAX. THRUPUT AVERAGE TERUPUT usec msec msec 300 3333 8S1.2 415.6 2400 416 106.4 53.2 9600 104 26.6 13.3 Figure 4 is a more detailed schematic diagram of the status/control multiplexer hardware shown in Figures 1 through 3. Components and interconnecting lines in Figure 4, which correspond to components and interconnecting lines in the block diagrams of Figures 2 and 3 are identified by corresponding labels. It should be recognized that multiplexers 4, 6, and 8 and output latches 18, 20 and 22 of Figures 2 and 3 are not shown in Figure 4 in order to simplify the diagram. However, the interconnecting lines associated with these components and the alphabetic labels shown in Figures 2 and 3 are shown in Figure 4.

As shown in Figure 4, multiplexer 2 receives 16 TTL alarm status inputs. Multiplexer 2, as noted above, is a type 74510 multiplexer. Multiplexer 2 also receives address inputs (A, B, C, and D) on lines G. The data output of the multiplexer 2 appearing on line H is coupled to pin P30 of UART 10 via a logic inverter 30.

Focusing on the circuitry that generates the address signals (A, B, C, and D) which are input to the multiplexer 2 (i.e., the control logic unit 12 shown in Figure 2), a clock frequency generator 32 generates a clock frequency signal of, for example, 7.3728 MHz. The clock signal generated by generator 32 is divided down by frequency divider 34 whose output is applied to the UART 10 at pins P17 and P40. The UART chip 10 which may, for example, be a type 1863 manufactured by Western Digital Corporation, requires a clocking signal which is 16 times the baud rate.

The output of frequency divider 34 is divided down by frequency divider 36 whose output is applied to frequency divider 38 which further divides the output signal to generate the A, B, C, and D signals which are the address outputs transmitted over lines G to the multiplexer 2. These address signals are additionally provided to UART 10 via input pins P26, P27, P28, and P29 for transmission.

The counter comprising frequency divider 38 which produces outputs A, B, C, and D serves to sequentially increment the output address such that the input lines are sequentially and repetitively scanned.

The high frequency output signal from frequency divider 36 (i.e., relative to the output of divider 38) is utilized to strobe the 4 address outputs A, B, C, and D into UART 10. In this regard, the output signal from frequency divider 36 is logically inverted by inverter 40 and coupled to one input of NAND gate 42. The other input of NAND gate 42 receives a signal from UART 10 via pin P22 which signal is generated when the UART 10 transmit register is empty. When both the signal from inverter 40 (which indicates that the address inputs are ready to be transmitted) and the signal from pin P22 are present at the input of NAND gate 42, the UART 10 is triggered to transmit.

In response to the signal received on pin P23, UART 10 operates to transmit the appropriate input TTL signals. The TTL signals are transmitted out of pin P25 of UART 10 and are delivered to converter 44 which converts the TTL signals from UART 10 to ASCII levels. Converter 44 is a conventional converter manufactured by Maxim Corporation, type MAX 232 which converts the TTL output signals from UART 10 to serial ASCII level (RS232). Converter 44 is also capable of receiving an ASCII level input signal and delivering a TTL signal to, for example, pin P20 of UART 10.

The control logic 14 shown in Figure 3 includes a one-shot multivibrator 46 which receives a signal from UART 10 on pin P19 which indicates that the UART 10 has just placed data in its output register. This signal initiates the firing of the one-shot 46 whose output signal on line U is used to strobe data into the output latches 16A or 16B via NAND gates 48 and 50. One-shot 46 also returns a signal to pin P18 of UART 10 which indicates to the UART 10 that the data has been latched and that UART 10 must prepare to receive the next word.

NAND gates 48 and 50 also receive an input from pin P9 of UART 10 which is the D address signal. This signal identifies which of the two 8 bit output latches 16A or 16B is to receive the output data. The D address signal enables either output latch 16A or 16B by being transmitted directly to NAND gate 50 and to NAND gate 48 via inverter 52. In this fashion, it is impossible to simultaneously enable both output latches 16A and 16B. The 16 alarm outputs generated at the output of latches 16A and 16B correspond to the 16 alarm inputs received at multiplexer 2.

Focusing briefly on the pins of UART 10, it is noted that UART 10 pin P1 is a power pin, and pins P3, P4, P16,'P21, P36 and P39 are ground pins. Pins P5-P20 of UART 10 are devoted to receive functions and pins P22-P39 are dedicated to transmit functions. As noted previously, pins P40 and P17 are 16x clock inputs which provide the clocking signals for UART 10 transmit and receive operations.

Pins P5, P6, and P7 are utilized for connection to the output latches 18, 20, and 22 shown in Figure 3. In this regard, note interconnecting lines W shown in both Figures 3 and 4. Correspondingly, pins P31-P33 receive inputs from the multiplexers 4, 6, and 8 shown in Figure 2 on correspondingly labelled input lines El, E2, and E3. Pins P34-P39 provide voltages necessary to generate the various logic levels required in UART 10. Pins P2, P13-15 and P24 are not utilized in the current exemplary embodiment.

An exemplary alarm unit which may be utilized, in conjunction with the multiplexer system described above, is shown in Figure 5. As shown in Figure 1, individual alarm units at the control site C may be associated with each of the system's remote sites S1-S3. An alarm unit operates based on information received from a remote site via the status and control system described above in conjunction with locally generated control signals. The alarm unit delivers a contact closure to operate a composite alarm indicator/enunciator and provides a detailed means of indicating the particular source of the alarm.

The alarm unit shown is Figure 5 includes exemplary logic circuitry that is utilized to logically combine status information received from a remote site and to generate a fault indicating signal in response to the logically combined status inputs. Additionally, the alarm unit responds to the actuation of predetermined control functions which are expected to generate a desired response at the remote site.

For example, if a remote transmitter is turned on by actuation of a transmitter-turn-on control function, a status change should be detected, indicating that output power is presently being detected. If such a response is not received within a predetermined period of time, then the alarm unit of Figure 5 generates a visual and/or audible alarm at the control site. If, however, the transmitter is off, but no transmitter control function had been initiated, the same status information will be received indicating that there is no transmit power at the predetermined transmitter, but this condition is not indicated as a fault by the alarm unit shown in Figure 5.

The exemplary alarm unit shown in Figure 5 has eight separate alarm initiating paths. Four of these paths look at the logical combinations of the locally generated transmitter PTT, excessive reflected remote transmitter power and the presence or lack of forward remote transmitter power. Three of the remaining four alarm path signals are in a form that can directly initiate alarms while the last detects the absence of received ASCII status data from the remote site.

Referring to Figure 5 in further detail, logical AND gate 60 will have all of its inputs held high (logic 1) if no faults are being detected. In this case, the output relay 62 is not operated and the external contacts 64 are not initiating an alarm indication. When any one or more of the inputs to AND gate 60 go low (logic 0), the relay 62 operates and the contacts 64 initiate an external alarm indication. Diode 65 serves as a transient suppressor.

Threshold detectors at the remote sites S1-S3 generate go/no go signals (i.e., logic 1 or logic 0) which are transmitted via the status and control system to the control site. These signals are all denoted as items 2A-2E on the block diagram. The meaning assigned to each is also shown in Figure 5.

Signals 2C, 2D, and 2E are logically utilized directly as received.

The LED's (and their associated current limiting resistors) 67, 68, 70, 72 and 74 provide, when lit, an indication of a fault source. The LED's 67, 68, 70, 72 and 74 are lit when they are forward biased upon the occurrence of a fault indicating condition, as can be seen from the logic 0 conditions labeled in Figure 5.

In order to have an indication that no data updates are being received from a remote site, a retriggerable one-shot multivibrator 66 has the status and control system serial ASCII format data signal 2F applied to its input. The time constant is so selected to cause the one-shot 66 output to remain in one state as long as data is being received. If for any reason the serial data ceases, the one-shot 66 changes state and an alarm is initiated.

The remaining source of alarm inputs is associated with detecting that the remote transmitters did not come on the air when they were so instructed. This is accomplished by the remote sensing of forward and reflected transmitter RF power and making logical decisions at the control site based thereon.

Specifically, if a transmitter is not keyed on the air, the locally generate PTT command 1 is sensed as a logic 0 which keeps the output of NAND gate 76 high independent of.the other inputs to gate 76. When the PTT command 1 is asserted, the associated logic input to gate 76 goes high (logic 1) however, the hold-off timer 78 is also started.

The hold-off timer output goes low for a short period of time which still keeps the output of gate 76 high. The purpose of this is to allow time for the remote transmitters to respond to the PTT signal 1 and to allow the RF sensor status information to be returned to the control site. Once the PTT line 1 has been asserted and the hold-off timer 78 has timed out, the presence of detected RF forward power 2B and the absence of reflected RF power 2A (as indicated by a signal from inverter 80) cause the output NAND gate 82 to be low (logic 0) which still keeps the output of NAND gate 76 in the non-alarm (logic 1) state. Should high reflected transmitter RF power 2A or inadequate transmitter forward power 2B be sensed1 the output of NAND gate 82 will go high, thus allowing all of the inputs to NAND gate 76 to be high, which subsequently initiates an alarm. Removal of the PTT signal 1 immediately causes the corresponding input of NAND gate 76 to go low, disabling any further alarm initiating capability of the Tx alarm detector circuit. A Tx alarm detector circuit would be employed for each remote transmitter. While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiments, it is to be understood that the invention is not to be limited to the disclosed embodiments, but on the contrary, is intended to cover various modifications and equivalent arrangements

Claims (48)

CLAIMS:

1. A communications system having a control site and at least one remote site, said control site communicating with said at least one remote site over a plurality of communication channels, said communications system comprising: a plurality of sensors associated with said at least one remote site, and multiplexing means for transmitting data relating to the status of said plurality of sensors to said control site over one path of a full duplex communications channel, said multiplexing means including means for receiving over the other path of said full. duplex communications channel control signals from said control site for controlling at least one function at said at least one remote site.

2. A communications system according to claim 1, wherein at least one of said sensors includes means for sensing whether a transmitter is producing a power output.

3. A communications system according to claim 1, where in at least one of said sensors includes means for sensing reflected antenna power.

4. A communications system according to claim 1, wherein said at least one remote site is in a building and wherein at least one of said sensors includes means for detecting a status condition related to said building.

5. A communications system according to claim 1, wherein said one of said communication channels is a single voice bandwidth channel.

6. A communications system according to claim 1, wherein said multiplexing means includes means for receiving logic level data from said plurality of sensors and for generating data in a predetermined machine readable format.

7. A communications system according to claim 6, wherein said logic level data is in TTL format and said machine readable format is ASCII.

8. A communications system according to claim 1, wherein said control site includes means for generating control signals for initiating control functions to be performed at said at least one remote site.

9. A communications system according to claim 8, wherein said control signals initiate a site controller reset operation.

10. A communications system according to claim 8, wherein said control signal initiates a transmitter test operation.

11. A communications system according to claim 8, wherein said means for generating includes means for disabling a remote transmitter.

12. A communications system according to claim 8, wherein said means for generating includes means for initiating testing operations at said remote site.

13. A communications system according to claim 1, wherein said one of said communication channels is an asynchronous ASCII data channel.

14. A communications system according to claim 1, further including display means responsive to signals received from said multiplexer means for displaying an indication of the state of at least one of said sensors.

15. A communications system according to claim 1, further including alarm means responsive to signals received from said multiplexer means for generating an indication of an alarm condition.

16. A communications system according to claim 15, wherein said alarm means includes means for logically combining signals received from said multiplexer means and for generating an alarm indication depending upon the state of the signals received from said multiplexer means.

17. A communications system according to claim 16, wherein said alarm means includes means for indicating when no data is being received from a predetermined remote site.

18. A communications system according to claim 1, wherein said multiplexer means further includes: at least one data input means having a plurality of data inputs and one data output; address control means coupled to said data input means for generating address signals for selecting data on one of said plurality of data inputs to be coupled to said data output; transmitting means coupled to said data input means and said address control means for transmitting the data appearing on said data output and said address signals.

19. A communications system according to claim 1, wherein said multiplexer means further includes: data and address receiving means for receiving data and address information; at least one demultiplexing means coupled to said data and address receiving means having at least one data input and a plurality of data outputs, said demultiplexing means including meahs for steering data received on said at least one data input to the data output identified by said address information.

20. In a communications system having a control site and at least one remote site, said control site communicating with said at least one remote site over a plurality of communication channels, a method for exchanging status and control information between said at least one remote site and said control site comprising the steps of: providing a plurality of sensors at said at least one remote site; transmitting data relating to the status of said plurality of sensors to said control site over one of said communication channels; and remotely controlling at least one function at said at least one remote site via signals transmitted over said one of said communication channels.

21. A method according to claim 20, further including the step of sensing whether a transmitter at said at least one remote site is producing a power output and transmitting an indication of same over said one channel.

22. A method according to claim 20, further including the step of sensing reflected antenna power and transmitting an indication of same over said one channel.

23. A method according to claim 20, wherein said at least one remote site is in a building and further including the step of detecting a status condition related to said building and transmitting an indication of said status condition over said one channel.

24. A method according to claim 20, wherein said transmitting step includes the step of receiving logic level data from a plurality of sensors and generating data in a predetermined machine readable format.

25. A method according to claim 20, further including the step of generating control signals at said control site for initiating control functions to be performed at said at least one remote site.

26. A method according to claim 25, further including the step of initiating a site controller reset operation.

27. A method according to claim 25, further including the step of initiating a transmitter test operation.

28. A method according to claim 25, wherein said step of generating includes the step of disabling a remote transmitter.

29. A method according to claim 20, further including the step of: displaying an indication of the state of at least one of said sensors.

30. A method according to claim 20, further including the step of generating an indication of an alarm condition at said control site in response to the receipt of predetermined status conditions.

31. A method according to claim 30, further including the step of logically combining signals received over said one of said communication channels and generating an alarm indication depending upon the state of the signals received from said at least one remote site.

32. For use in a communication system having a control site and at least one remote site, said control site communicating with said at least one remote site over a plurality of communication channels, multiplexing apparatus comprising: at least one multiplexer means having a plurality of data inputs and one data output; address control means coupled to said multiplexer means for generating address signals for selecting data on one of said plurality of data inputs to be coupled to said data output; transmitting means, coupled to said multiplexer means and said address control means, for transmitting the data appearing on said data output and said address signals.

33. Multiplexing apparatus according to claim 32, wherein said data received by said multiplexer means defines the state of status points associated with said at least one remote site.

34. Multiplexing apparatus according to claim 32, wherein said at least one multiplexer means includes a plurality of multiplexer means, each having a plurality of data inputs and one data output, each of said data outputs being coupled to said transmitting means.

35. Multiplexing apparatus according to claim 34, wherein each of said plurality of multiplexer means is coupled to said address control means for simultaneously receiving said address signals.

36. Multiplexing apparatus according to claim 32, wherein said transmitting means generates output data in a predetermined machine readable format.

37. Multiplexing apparatus according to claim 36, wherein said machine readable format is ASCII.

38. Multiplexing apparatus according to claim 32, wherein said at least one multiplexing means includes means for receiving logic level data.

39. Multiplexing apparatus according to claim 32, wherein said address control means includes means for scanning each of said plurality of inputs.

40. Multiplexing apparatus according to claim 32, wherein said transmitting means includes means for transmitting the identity of the input line being scanned and the corresponding data present on the scanned input line.

41. Multiplexing apparatus according to claim 32, wherein said address control means includes means for defining the rate at which said input lines are scanned.

42. Multiplexing apparatus according to claim 34, further including means for providing output data from each of said plurality of multiplexer means in parallel to said transmitting means.

43. Multiplexing according to claim 32, wherein said address control means includes means for incrementing said address signals for repetitively identifying each of said plurality of inputs.

44. For use in a communications system having a control site and at least one remote site, said control site communicating with said at least one remote site over a plurality of communication channels, demultiplexing apparatus comprising: receiving means for receiving data and address information; at least one demultiplexing means coupled to said receiving means having at least one data input and a plurality of data outputs, said demultiplexing means including means for steering data received on said at least one data input to the data output identified by said address information.

45. Demultiplexing apparatus according to claim 44, wherein said at least one demultiplexing means includes a plurality of demultiplexing means, each of said demultiplexing means being coupled to simultaneously receive said address information.

46. Demultiplexing apparatus according to claim 44, further including control means coupled to said receiving means and said at least one demultiplexing means for strobing received data o said at least one demultiplexing means.

47. A communications system substantially as hereinbefore described with reference to Figure 1 optionally as modified by Figure 2 or Figure 3, Figure 2 or 3 being optionally as modified by Figure 4 and/or 5.

48. A multiplexer substantially us herein before described with reference to Figure 2 and 3 optionally as modified by Figure 4.