CONTROL SYSTEM USING TIME DIVISION MULTIPLEXING

Abstract: A control system for selectively communicating a plurality of sensors (17) with associated remote control devices (19, 20) includes a Master Synchronizer (10), a transmitter (11, 12) for each sensor and a receiver (13 14a) for each control device. A single signal line (14) is connected to all transmitters (11, 12) and receivers (13, 14a), and a single synchronization line (15) couples the Master Synchronizer (10) to all transmitters and receivers. The Master Synchronizer (10) generates a time frame signal which has a reset portion for resetting all transmitters and receivers synchronously at the start of each frame, and a periodic portion which determines the time slots for each frame and which decrements counters (31, 38) in all transmitters and receivers synchronously. A time division multiplex system is used to communicate each transmitter with one or more associated receivers during a predetermined time slot of a periodic time frame determined by the Master Synchronizer.

Description: CONTROL SYSTEM USING TIME DIVISION MULTIPLEXING BACKGROUND AND SUMMARY The present invention relates to control systems; and more particularly, it relates to control systems wherein a number of individual sensors (a thermostat, for example) are used, and it is desired to selectively communicate each sensor with one or more control devices associated with that sensor. Control systems of this type may be used, for example, in large buildings where it may be desired to integrate all of the heating, ventilating, cooling, and even secto ity systems into a single master system. The present invention includes a transmitter for each sensor, a receiver for each control device and a Master Syncronizer. A single signal line is connected to all trans¬ mitters and receivers; and a single synchronization line couples the Master Synchronizer to all transmitters and re¬ ceivers. The Master Synchronizer determines the overall time frame or operating cycle of the system, and the signal it transmits includes a periodic signal portion and a reset signal portion. Each cycle of the periodic signal defines a time slot in the time frame, and the reset signal portion is used to reset the Master Synchronizer and all transmitters and receivers at the same time, thereby achieving overall synchronization. Each transmitter and one or more associated receivers are allocated a predetermined time slot of the time frame, during which time slot the transmitters communicate with their associated receivers. A decrementing counter is provided for each trans¬ mitter and each receiver. At the beginning of each frame, these counters are set to a predetermined number representa¬ tive of the time slot allocated to those units. When the counter is decremented to zero, a time slot is defined for communicating a transmitter with its associated receivers. Thus, a transmitter is permitted to send a signal along the signal line to all receivers associated with it, and this signal causes a response only in those receivers whose counters have been decremented to zero during the same time slot. In the preferred implementation, this communica¬ tion occurs once every time frame. The Master Synchronizer also includes a decrementing counter, and when it reaches zero the transmission of syn¬ chronization ("sync" for short) signals to all transmitters and receivers is inhibited for a predetermined time. Thus, the absence of sync pulses is used as a reset signal to reset the Master Synchronizer and all transmitters and receivers once each time frame. An energy-containing signal, rather than the absence of a signal, is required to actuate a control device. This reduces error in the event of line interruption or power failure. THE DRAWING FIG. 1 is a functional block diagram of a system incorporating the present invention; FIG. 2 is a circuit schematic diagram, partly in functional block form, of a Master Synchronizer used in the system of FIG. 1; FIG. 3 is a circuit schematic diagram, partly in functional block form, of a transmitter in the system of FIG. 1; FIG. 4 is a schematic diagram of circuitry which interfaces a control input with the transmitter of FIG. 3; FIG. 5 is a circuit schematic diagram, partly in functional block form, of a receiver for actuating a control device in accordance with FIG, 1; and FIG. 6 is a timing diagram illustrating various operating waveforms in the system, DETAILED DESCRIPTION Referring first to FIG. 1, the system includes a Master Synchronizer which is enclosed within the dashed line 10, a plurality of transmitters, two of which are shown and enclosed within the dashed lines 11, 12, and a plurality of receivers, two of which are shown and enclosed within the dashed lines 13, 14 respectively. Persons skilled in the art will appreciate that the system is not limited to any particular number of transmitters or re¬ ceivers, and that the number of transmitters may be different ξ* * tA~ 0,' PI than the number of receivers, A signal line 14 is connected to all of the transmitters and receivers; and a sync line 15 is connected to the Master Synchronizer 10 and all of the transmitters and receivers. As will be more fully explained below, the Master Synchronizer 10 generates a synchronization and timing sig¬ nal which is coupled to all of the transmitters and all of the receivers. This synchronization and timing signal in¬ cludes a reset portion and a periodic portion, both of which form a complete cycle or "frame". The reset signal portion of the signal is used to reset the Master Synchronizer and all transmitters and receivers at the beginning of each frame; and the periodic portion of the signal is used to define time slots within the frame. Each transmitter and its associated receiver or receivers is assigned or allocated a particular time slot during which time that transmitter communicates with all of its associated receivers via signal line 14. For example, the Master Synchronizer may define 256 time slots each frame, and by convention, these are numbered 0 through 255. The last time slot, namely 255, is reserved for system protection and utilization by the Master Synchronizer for frame detection. Supposing, then, that transmitter 11 in FIG. 1 is assigned time slot 0, then during that time slot it would communicate with as many receivers as may be desired by means of an information signal transmitted along the signal line 14. This transmitter and all of its associated receivers obtain common timing information from the sync line 15. Another transmitter and its associated receiver or receivers may be assigned time slot 1, and so on, up to transmitter No. "M" designated 12 in FIG. 1. Each of the transmitters has associated with it a sensor device, and these are designated 17 and 18 in FIG. 1 respectively for the transmitters 11, 12. Further, each of the receivers is connected to a control device, and these are designated 19 and 20 respectively for the receivers 13, 14. Each of the transmitters is similar in structure and operation, as is each of the receivers. The only dif¬ ference in transmitters is the information or signals stored __Oi\\Pl - wip to identify its time slot, and the same is true for receivers, hus , a complete understanding of the invention can be ob¬ tained from a description of only one transmitter and one receiver. Still referring to FIG. 1, the Master Synchronizer includes a master encoder22 having a plurality of binary - outputs defining the number of time slots in a frame. These outputs are connected In parallel to the inputs of a decre¬ menting counter 23. A master oscillator 24 generates a periodic signal coupled through a line driver circuit 29 to the sync line 15. The sync signal is received (after suit¬ able filtering) by a clock flip flop 25 and a reset timer 28. The clock flip flop 25 divides the frequency by two and generates a signal labeled CLK on line 26 to decrement the counter 23. The output of the reset timer is used to load the contents of the master encoder 22 into the counter 23 at the beginning of each time frame. Briefly, the Master Synchronizer operates as follows. The output of the master oscillator 24 is coupled to the flip flop 25 (via the sync line) which is used as a "divide by two" circuit to decre¬ ment the counter 23. When the contents of the counter 23 is decremented to zero, an output signal from the counter is used to inhibit the master oscillator 24 from producing further timing pulses . The absence of timing pulses on the sync line over a predetermined period is sensed by the reset timer 28, and at the end of that predetermined period, it generates a signal which loads the contents of the master encoder into the counter 23 . thus releasing the master oscillator and initiating a new frame. Turning now to the transmitter 11, it includes an encoder 30, having its ouptuts connected in parallel to the Inputs of a decrementing counter 31. The signal from the sync line 15 is coupled to the clock input of a CLK flip flop 32 and to a reset timer 33. Persons skilled in the art will appreciate that suitable filtering, well known in the art, may be used at all locations where signals are derived from either the signal line 14 or the sync line 15. The "1" output of the flip flop 32 is used to decrement the counter 31; and complementary outputs from the flip flop 32 are connected to gate circuits 34. The output of the reset timer 33 is used to load the contents of the encoder 30 into the counter 31 at the beginning of each frame. The output of sensor 17 is connected to the gate circuits 34, and the output of the gate circuits is coupled through a line driver 35 to the signal line 14. Briefly, the transmitter operates as follows. The sensor 17 generates a binary signal—that is, the output of the sensor 17 is in one of two states. In its more general aspects, however, the invention is not limited to the use of binary sensors, but most sensors in commercial use for which the invention is presently intended fit this category. The output signal of the sensor 17 (in complementary form) is fed to the gate circuits 34 and is present at all times. The absence of pulses on the sync line 15 defines the reset signal portion of the sync signal; and the reset timer 33 detects this reset signal portion of the sync signal, and loads the contents of the encoder 30 into the counter 31. The contents of the encoder 30, as mentioned above, is a ' binary word representative of the time slot allocated to transmitter No. 1. After the counter 31 is loaded and sync pulses are transmitted on the sync line 15, the CLK flip flop 32 decrements the counter 31. When the counter 31 reaches a count of zero, an enable signal is fed to the gate circuits 34. The output of the flip flop 32 is combined in the gate circuits 34 with the output of the sensor 17 and enabled by the output of the counter 31 to transmit an ON signal during the CLK (true) period and an OFF signal during the CLK (not) period. In this manner, a failure that would cause the sensor signal to be high during both CLK and CLK period- will result in an "OFF" signal to the load or control device. In other words, ambiguous signals result in an off condition at the control device. Further, the absence of a signal during both the CLK and CLK periods does not affect the existing state of the control device--if it is on, it stays on; and if it is off, it stays off. Referring now to the receiver 13, it Includes an encoder 37 similar to the previously described encoders 22 and 30, and having a plurality of outputs connected in par¬ allel to the inputs of a decrementing counter 38. The coun¬ ter 38 generates a signal when its contents is decremented to zero, and this signal is fed to the inputs of gates 39, 40, the outputs of which feed respectively the JK inputs of a flip flop 41. The output of the flip flop 41 is used to activate the control device 19. The receiver 31 includes a reset timer 42 which is responsive to the reset signal por¬ tion of the sync signal for loading the contents of the encoder into the counter 38. The receiver also includes a CLK flip flop 43 which is responsive to the periodic signal portion of the sync signal for decrementing the counter 38 and for feeding a strobe signal generator 45. The comple¬ mentary outputs of the flip flop 43 are also fed to the gates 39, 40 respectively, as illustrated. The receiver operates as follows . The reset timer 42 is responsive to the reset signal portion of the sync signal for loading the contents of the encoder 37 into the counter 38. Thereafter, the periodic portion of the sync signal is fed to the flip flop 43 to decrement the counter 38. When the counter 38 is decremented to zero, it sends an enable signal to the gates 39, 40. The actuation signal on the signal line 14 is also coupled to the gates 39, 40, and at the appropriate time (determined by strobe generator 45) during the time slot allocated to Receiver No. 1, the signal on line 14 is gated through the gates 39, 40 to the flip flop 41 from which it is used to activate the control device 19. The strobe signal is derived by delaying the sync signal, as will be explained. As a result, If both inputs to flip flop 41 are low at strobe time, its output remains unchanged. If gate 39 is enabled at strobe time, flip flop 41 is set; and if gate 40 is enabled at strobe time, flip flop 41 is reset. The control device 19 is controlled accordingly. The counters of the Master Synchronizer and all transmitters and receivers are reset at the beginning of OΛ-PI A -. VV1JPPOO each time frame; and in the preferred embodiment, this is accomplished by sensing the absence of periodic synchroniza¬ tion signals. If it is desired to have the control device 19 actuated by sensor 17, then the contents of encoder 30 and the contents of encoder 37 are made identical. The con¬ tents of these two encoders may be established by direct wiring, the use of manually controlled switches, semiconduc¬ tor switches, or any number of other techniques. It will also be appreciated that any number of receivers may be allotted to the same time slot and thereby controlled by the same sensor. One advantage of the present invention is that a given receiver may be assigned to a different transmitter simply by changing the contents of its encoder. Conversely, a given transmitter may be assigned to a different receiver in the same manner. Referring now to FIG. 2, the master oscillator includes a comparator 50 having its output connected to the clock (C) input of a flip flop 51. A 5 kHz sync signal is fed through a filter section 55. The discharge path of a capacitor 61 includes a resistor 59 since the diode 63 is reversed-biased. Hence, the charging time of the capacitor 61 is much shorter than its discharge time. The output of the comparator 62 is a signal referred to as JAM; and this signal is coupled to the counter 23 to load the contents of the master encoder 22. The signal INIT is used to hold the counter 23 and the oscillator 24 for an initial period of time (tl on line L7 of FIG. 1) until the power supply levels have sta¬ bilized. When the signal INIT goes low, the signal OSCN also goes low and the signal OSCP goes high. The oscillator 24 will not commence oscillation for a second time delay identified as time T2 in line L2 of FIG. 6. The output signal from the counter 23 which is fed to the NAND gate 73 is generated when the counter is decremented to zero and it is a low signal which changes the states of OSCN and OSCP, thereby terminating operation of the oscillator 50 when the counter 23 is decremented to zero. The number of time slots in a given frame is deter¬ mined by the master encoder 22. In the event that the master encoder 22 is inoperative, resistor 79 will force the coun¬ ter to the maximum count of 256, and the system will still operate. The signal OSCN is used to reset the flip flop 51, and It is also coupled through a delay circuit comprising resistor 76 and capacitor 77 which determine delay time T2 of line L2 of FIG. 6 (as well as the frequency of oscilla¬ tion) , to the oscillator 50 to commence oscillation. The signal on line L3 of FIG. 6 is the shaped sync signal at the output of comparator 58. Flip flop 25 ignores the first clock signal and it is held with the CLK output high because the JAM signal causes it to remain in the set condition. The JAM signal is therefore released as shown in line L4 of FIG. 6 after a time constant T4 defined by the values of resistor 60 and capacitor 61. The JAM signal will remain low as long as incoming pulses are received to charge capa¬ citor 61 at a rate faster than charge leaks off the-- capaci¬ tor. This will cause the plus input of comparator 62 to remain higher than the V-n fed to the negative input. The resulting JAM signal, when it occurs as indicated in line L4, causes the counter 23 to be loaded with the contents of the master encoder 22. With the JAM signal thus released after the first positive excursion of the output of the comparator 58, the flip flop 25 will respond to subsequent positive-going lead¬ ing edges to generate the CLK signal seen in line L5 of FIG. 6. The CLK signal thus corresponds to the sync signal counted down by a factor of 2. The CLK signal from the flip flop 25 is, as mentioned, coupled via line 26 to decrement the counter 23. When counter 23 Is decremented to zero, the signal DECODE goes low. This signal, inverted, is shown on line L12 of FIG. 6; and when it goes low, it changes the output state of gate 73, thereby changing the states of signals OSCN and OSCP. This action terminates operation of the oscillator 50 and immediately resets the flip flop 51, thereby causing the 5 kHz sync signal to go negative as indicated at 86 on line L2. Then the signal JAM will go low, to re-load the contents of the master encoder 22 into the counter 23. This longer delay is defined as time constant T5 in FIG. 6. At the same time, the output of the gate 66, namely the signal JAM inhibits operation of the flip flop 25 for the first cycle of the next frame. The JAM signal sets the CLK flip flop in transmitters and receivers, as well, for these reasons: (a) if the CLK is falsely triggered, the JAM signal brings it back into synchronism with the rest of the system on the next frame; (b) to insure that the CLK flip flop is in a known state when power is turned on; and (c) the first sync pulse derives the strobe for CLK "true" DECODE "0" to protect against ambiguities that would occur if the transmitted signal remained high. Turning now to FIG. 3, the transmitter is similar in operation to the master encoder just described in many of its aspects. . The absence of sync pulses permits capacitor 112 to discharge, and after a predetermined time, the JAM signal will go low, thereby loading the contents of the encoder 90 into the counter 91. The signal CLK is used to decrement the counter 91 after it is loaded with the contents of en¬ coder 90; and when the counter 91 is decremented to zero, it generates the signal DECODE, and this signal is used to generate an enable signal to the gates 95, 96. ' If the sig¬ nal SWON is positive, then the one output of flip flop 98 is positive and during the positive half cycle of CLK, the gate 95 will generate a pulse such as the one shown (inver¬ ted) on line L7 of FIG. 6 during the first half cycle of the CLK signal during the time slot associated with that parti¬ cular transmitter. If the output of the sensor is a zero or low signal, then the zero output of the flip flop 98 is high. During the next cycle of the signal CLK,the gate 96 will generate a pulse such as the one shown (also inverted) on line L8 of FIG. 6. FIG. 4 shows a circuit schematic diagram for the logic power supply. Turning now to FIG. 5, the receiver receives the 5 kHz sync signal from the sync line 15. The output of com¬ parator 156 comprises the signal JAM for the transmitter. The delay circuit 159 delays the input to the com¬ parator such that the strobe signal occurs at approximately the 40% point of the CLK and CLK periods, see line L9 of FIG. 6. This timing may be compared with the CLK signal of FIG. 5 since even though the CLK signal is locally generated in the Master Synchronizer, each transmitter and each re¬ ceiver, these signals will nevertheless all be in synchronism because they are derived from the same Incoming sync pulse on the sync line 15. If the input signal is "true" or "one" as indicated on line L7 of FIG. 6, then a strobe pulse such as the one designated 190 occurring in the first half cycle of the local clock signal will cause the "one" output of the flip flop 176 to go "high" as at 191 on line L10. Similarly, If the input signal had been "false" or "zero" as indicated on line L8 of FIG. 6, then the "zero" output of flip flop 176 will go high when the strobe pulse 192 clocks the flip flop 176, the output being indicated on line Lll, and going high at 193. In either case, as Indicated above, an energy- containing pulse is required toactuate the flip flop 176, as well as the photocouple 179. In operation, when an in¬ coming signal causes the photocouple to conduct, SCR 191 also conducts. This, in turn, will cause current to flow through bridge 192 and resistor 197 to apply a gate voltage to cause the triac 194 to conduct, thus connecting the load to the ac source.

Claims: CLAIMS 1. In a multiplex system for communicating a sensor device with a remotely located control device including a synchronization line; and a signal line; the improvement characterized by master synchronization circuit means for generating a synchronization signal coupled to said synchro¬ nization line, said synchronization signal being generated each time frame and including a periodic signal portion and a reset signal portion, each cycle of said periodic signal portion defining a time slot in said time frame; a plurality of transmitters, each including trigger- able counter circuit means and being connected to said synchronization line and said signal line and responsive to said reset signal portion of said synchronization signal for loading a predetermined count representative of an assigned time slot into said counter means, said synchronization sig¬ nal portion being " operative to trigger all transmitter coun¬ ter circuit means simultaneously, each transmitter further including gating circuit means responsive to said counter circuit means reaching a predetermined count for coupling an output signal of said sensor to said signal line; and a plurality of receivers, each including triggerable counter circuit means and being connected to said synchroni¬ zation line and said signal line and responsive to said reset signal portion of said synchronization signal for load¬ ing a predetermined count representative of an assigned time slot into said receiver counter means, said periodic signal portion being operative to trigger all of said receiver counter circuit means simultaneously, each receiver further including output circuit means responsive to said counter circuit means reaching a predetermined count for coupling a signal on said signal line to an associated control device during the time slot associated with that receiver. 2. The apparatus of claim 1 wherein said master synchronization circuit means includes oscillator circuit means responsive to a control signal for generating said periodic signal portion when said control signal is in a first state and for generating said reset signal portion when said control signal is in a second state, said synchronization circuit means further including triggerable counter circuit means for generating an output signal when the contents thereof reach a predetermined count at least as great as the number of time slots in a frame; reset circuit means responsive to the absence of an output signal from said oscillator means for a predetermined time for loading said counter circuit means to a predetermined count for initiating an operation of said oscillator circuit means; circuit means for triggering said counter circuit means responsive to the periodic signal portion of said synchro¬ nization signal, the output signal of said counter circuit means inhibiting further operation of said oscillator cir¬ cuit means until said counter circuit means is re-loaded by said reset by said timer circuit means. 3. The apparatus of claim 2 wherein said reset signal portion of said synchronization signal consists of the absence of periodic signals from said oscillator circuit means. 4. The apparatus of claim 2 wherein each of said transmitters and receivers further includes reset timer circuit means responsive to said reset signal portion of said synchronization signal for re-loading associated coun¬ ter circuit means, the reset signal time of said Master Synchronizer being longer than the reset signal time of said transmitters and receivers. 5. The apparatus of claim 1 wherein said system includes a plurality of sensor devices capable of generating a binary signal having first and second states, and a plu¬ rality of control devices capable of responding to a binary signal having first and second states, each transmitter including clock circuit means responsive to said periodic signal portion of said synchronization signal for generating a clock signal; output gate circuit means responsive to the output signal of said transmitter counter circuit means and to the binary output signal of an associated sensor device and to said clock signal for generating a first output pulse signal on said signal line during one portion of said clock signal if said sensor device is in a first binary state and O for generating a second output pulse signal on said signal line during a second portion of said clock signal if said sensor device is in said second binary state. 6. The apparatus of claim 5 wherein each of said receivers includes clock circuit means for generating a clock signal; strobe generator circuit means responsive to said clock signal for generating a strobe signal a pre¬ determined time after said clock signal; output gating cir¬ cuit means responsive to the output signal of said receiver counter circuit means and the receiver clock signal and the signal on said signal line from an associated transmit¬ ter; and output circuit means responsive to said gating circuit means and to said strobe signal for generating a first signal if the sensor of an associated transmitter is in a first binary state and a second signal if the sensor associated with said transmitter is in a second binary state. 7. The apparatus of claim 1 wherein each of said master synchronization circuit means includes decrementing counter circuit means; encoder circuit means for storing signals representative of the number of cycles desired in said periodic signal portion of said synchronization signal; master oscillator circuit means for generating an oscilla¬ tory signal only when said counter circuit means is not decremented to zero; reset timer circuit means responsive to the absence of an output signal from said master oscil¬ lator circuit means for a predetermined time for re-loading the contents of said encoder circuit means to said counter to re-initiate a time frame; and clock circuit means res¬ ponsive to the output signal of said master oscillator means for decrementing said counter means.

Inventors: MORELAND C
Applicants: CONTROL JUNCTIONS, CONTROL JUNCTIONS INC
Application year: 1978
Main classification: H04J3
IPC codes: G08C15, H04J3, H04L7, H04Q9