Patent GB-1265276-A (GB)
IPC: H04L12/423
Filed: 1970-04-01
Abstract: 1,265,276. Signalling between central and remote stations. NORTH AMERICAN ROCKWELL CORP. 1 April, 1970 [23 June, 1969], No. 15478/70. Heading G4H. A digital time multiplexing system comprises a master station 11, Fig. 1, and a number of serially connected remote stations 14, 15 &c. interconnected by a single line 12, 13 for transmitting signals between the master station and the remote stations, a remote station being operatively coupled to the master station only when it is in the " active mode," the signals otherwise being passed on to the next remote station so that signals passing between the master station and an active remote station pass through the intervening stations. The line 12, 13 forms a loop and the master station can transmit in either direction round the loop. The signal sent consists of 16 negative clock pulses 30 and positive data pulses 21 following specified clock pulses. Each remote station is as shown in Fig. 3 the two sides of the circuit being symmetrical, the units in operation depending on the direction of the signals. If the signals are passing from left to right they appear on line 12 and are applied to clock detector 30a, which responds to the negative pulses to pass the clock pulses to gate 47b, direction detector 31 and counter 35. The input pulses also pass to data detector 31a responding to the positive data pulses to apply timed data signals to command control 40. The direction detector comprises a flip-flop which is set to R if the pulses are passing from left to right and to R(L) if they are passing from right to left i.e. if they are on line 13. The R output enables gate 47b and if counter overflow signal OF is present the clock pulses are re-applied to line 13 by clock switch 50b connected to a negative source. The operation in the opposite direction is exactly the same. Counter 35 counts 16 clock pulses from either direction, the count being decoded by gate circuit 37. Specified counts in each sixteen pulses cycle are set aside for receiving data. These are combined in an OR gate to give a " bit receive" signal BR which is used to control the gates 70a, 70b. The particular decoded count signals control the command control unit 40 gating instructions to the appropriate devices 41 to be controlled. Other counts are not " bit receive " counts and these can be used for sending data from source 42 back to the master station over line 12. These data signals are applied via data switches 45a, 45b back on to the lines 12 or 13. When the counter 35 reaches an overflow condition the signal OF appears enabling all dates 47a, 47b and 70a, 70b. The remote station is then no longer actively coupled with the master station but serves merely to pass the signals on to the next station. The clock signals pass via gates 47a or 47b according to direction and the data signals pass via gates 70a or 70b according to direction. When all the remote stations have been coupled to the master station in their turn, the master station sends out signals in the other direction counting the counters down from the overflow conditions to the zero overflow. The remote stations are accordingly interrogated first in one order and then in the opposite order. A single break in the connecting wire therefore does not isolate any remote station from the master station.