Abstract: Time-multiplex programmable switching apparatus for establishing on demand time shared connections between pairs of ports. Signals within the system are digital. The invention is described in the context of an electronic private automatic branch exchange (EPABX) telephone system. A central processor unit (CPU) including a recirculating memory carries port address pairs and digital information to be exchanged along with a status word used for identifying program loops. Program steps are sequenced or initiated by timing signals and signaling data from the port units. Common buses interconnect the port units with the central processor unit. Port units are grouped with a common buffer memory for converting parallel data from the CPU to serial form. The CPU memory includes slots for housekeeping functions to detect, inter alia, an off-hook telephone. The principles of the invention are applicable to telephone central offices and digital switching systems as for computers, for example.