Abstract: A pulse code modulation (PCM) time division multiplex (TDM) automatic telephone exchange, comprising a series-to-parallel converter having incoming multiplex channel inputs and outputs, corresponding to the number of bits in a bit-group, a routing network having M inputs, each connected to an output of the series-to-parallel converter and a like number of outputs, and having a storage device therein, for simultaneously time and space switching information received in an incoming time slot to an outgoing time slot, and a parallel-to-series converter receiving a bit-group of one of the outgoing time slots on said M routing outputs. The operation of the telephone exchange is controlled by a time based device which synchronizes bit-group transfer in the routing network, the series-to-parallel converter, and the parallel-to-series converter, and also produces a periodic resynchronizing pulse.