Schaltungsanordnung für eine Teilnehmerstelle eines Pulscodemodulationssystems, dessen Teilnehmerstellen zu einem Ring zusammengeschlossen sind

1,182,363. Substation circuits. STANDARD TELEPHONES & CABLES Ltd. 26 July, 1968, No. 35856/68. Heading H4K. A subset for a looped PCM communication system comprises a stepping register 20 on to which all circulating codes are displayed while the subset is in the standby condition during which time the codes are inspected by an empty channel code detector 28 should the subset require a free channel for a call and are inspected by a subset number detector 22 should the code of the subset be circulated round the loop as a calling condition, detection of a code either by 22 or 28 operating a bistable 29 so that a store 30 records the position of the associated channel in a system cycle and so that a counter 25 synchronized by the bit stream on the loop operates a gate 21 repetitively for the duration of that channel so that the subset in that channel terminates the code arriving over the loop and substitutes a code read serially off the stepping register 20. The codes sent from 20 originate from a pushbutton set 26, on which calling codes are set up, or from a microphone encoder 37. Received codes when the subset is calling are the sent codes returned round the loop either unmodified (station busy) or modified (station being rung) and circuit 32 monitors these conditions with control over decoder 34 to connect appropriate ringing or busy tone to the earpiece 35. A clock 23 driven by the bit stream on the loop drives a synchronizing code detector 24 which with the appearance once each cycle of a synch. code zeros a channel counter 25.