APPARATUS FOR ENCODING AND TRANSMITTING SIGNALS

Serial information bits are represented by a signal which alternates between two levels and remains at each level for a time representative of the information bit being represented. The serial bits are produced by sampling of a set of parallel bit signals. Parallel signals which are to be converted to serial form by sucessive time-multiplex sampling (96) are divided into two sets, a low-priority set which changes infrequently and hence requires resampling at low rate, and a high-priority set which changes rapidly and requires prompt sampling upon the occurence of a change in signal value. The low-priority signals are sampled and transmitted sequentially at a low rate, but upon the occurence of a change in any of the set of high-priority signals, the sampling and transmission of the low-priority signals is interrupted and the high-priority signals are sampled and transmitted instead, after which sampling and transmission reverts to the low-priority signals.