Abstract: A time division multiplex switching module consisting of a serial-to-parallel multiplexer, a speech store, a parallel-to-serial demultiplexer and a control store serving eight incoming and eight outgoing t.d.m. lines. The module has a code detector, located on its input side, for detecting a mark code, and a code generator, located on its output side, for generation either the mark code or idle code. Control words in the control store include two extra bits, an input busy bit and an output busy bit to indicate busy paths through the module. When a mark code is detected by the code generator on a particular incoming line a mark present bit is set in a register (one of six) and the code generator is caused to generate mark codes on all the free outgoing lines. A number of modules are incorporated in a digital switching network arranged in the form of an array and a path can be set-up through the array.