still for kopplingssignalgivning between digital abonnentapparater and endformedlingsstationer in a pcm - tidsmultiplextelenet

摘要

1480257 Automatic exchange systems SIEMENS AG 24 Sept 1974 [27 Sept 1973] 41424/74 Heading H4K In a PCM, TDM system of the type in which subscriber stations are coupled to a concentrator using respective two wire lines and the concentrator is coupled to an exchange using TDM highways, speech and signalling information is transmitted between a subscriber station and the concentrator in the form of PCM words coded using a pseudoternary code i.e. a code in which binary 0 is represent by a zero voltage level and binary 1 is alternately represented by a positive voltage level and a negative voltage level. The PCM words transmitted on the subscriber lines comprise two bits of which the first bit is always 1 and sets as a word start signal. Bit 2 is used to indicate the type of PCM word i.e. speech, test code, signalling information &c. as shown in Fig. 1. These first two bits are removed in the concentrator before the word is transmitted on to the exchange, the PCM highways using 8 bit word time slots. There is also described with respect to Fig. 2, not shown, subscriber station circuitry for writing incoming PCM codes into a shift register, the start bit of the PCM word being used to energize a pair of counters driven by a subscriber clock, one counter providing stepping pulses for the shift register and the second counter counting the stepping pulses to cause the stepping to be stopped after 10 stepping pulses.