GB1417325A - Method of indicating slippage during data transmission - Google Patents

Abstract

1417325 Digital transmission; synchronizing INTERNATIONAL STANDARD ELECTRIC CORP 14 Feb 1973 [14 Feb 1972] 7186/73 Heading H4P In a method of determining 'slippage' along a transmission line, a check signal is transmitted either along the same or different channel to the data, signal values differing in adjacent intervals in a determined manner which provides check on reception that the sequence is correct, any departure being indicative of slippage. A series of alternate 0 and 1 check signals are transmitted as additional bits parallel or serial to data items, i.e. bit, word, or block, the signals on reception being fed through a terminal E to flip-flop FF and one input of exclusive OR gate EO, also to a clock generator TG. The state of FF is changed by clock signals T which are synchronized with and have double frequency of check signals and may be derived from check signals. Output K<SP>1</SP> is shifted relative to input Ke by one clock unit and inverted. A slippage signal S appears only if a received signal is not in agreement with the inverted previous check signal. In an alternative arrangement, a cyclic sequence of +1, 0, -1 is used which are represented by 3 pairs of binary values developed by a circuit, Fig. 4 (not shown), the fourth pair not being used in the arrangement, but may be used for other purposes, not particularly disclosed. In Fig. 5, the check signal is applied to comparators V1, V2 also to clock generator TG whch generates signals for the expected period of slippage, and controls a counter Z; this delivers a sequence of signal elements RKS which correspond to, are synchronized, but may be out-of-phase with received check signals. Modulator M develops outputs n + 1, n - 1 which are compared in V1, V2 and in the event of no slippage, outputs do not appear at A, W. However, if there is erroneous repetition V1, V2 will have different values from the modulator output hence a slippage signal will appear on A, W.