1. A time-division multiplexing system control unit adapted for use with a plurality of I/O units, said I/O units each associated with at least one respective multiplex channel, said control unit comprising: a logic unit operative to generate timing signals for the I/O devices, said timing signals comprising: a plurality of clock signals grouped in sets, each set of clock signals associated with a separate respective one of the I/O units; a plurality of first synchronization signals grouped in sets, each first synchronization signal interposed between two adjacent sets of clock signals such that the first synchronization signals mark boundaries of the sets of clock signals; a plurality of second synchronization signals, each second synchronization signal interposed between two adjacent sets of the first synchronization signals such that the second synchronization signals mark boundaries of the sets of first synchronization signals.