Abstract: A synchronous digital data switching apparatus in the form of a PABX telephone system is disclosed. The extension telephones of the apparatus are fully digital and transmit synchronous digital data to the switch. The switch includes a detector for scanning the inlets and remains connected to each inlet until the state of that inlet or a code is detected. Consequently the size of the switch is limited by the speed of available technology as all inlets must be examined within the minimum signalling period of any inlet. The telephones continually transmit digital data relevant to their state and also transmit digital codes during signalling. The apparatus is processor controlled and a switch memory for setting up connections between any inlet and any one or more outlets is time shared between the switch and processor.

Abstract: A digital control processor for controlling a number of relay sets from digital information received from a digital PABX. The digital control processor consists essentially of a first-in first-out memory and a combinational logic unit. The memory stores information relevant to an operation to be performed by the processor and re-cycles the information until the operation has been performed. The memory determines the action of the combinational logic unit which action includes changing the state of one of the relay sets. The action of the combinational logic unit is determined by time varying data states from the memory and/or from a relay set or sets. The digital control processor acts as an interface device between the digital/electronic world of the PABX and the analogue/mechanical world of the public exchange. The device receives digital information from a processor in the PABX and also monitors the current state of all the relay sets.