The SA9401 operates in conjunction with a standard EPROM to generate the system tone plans for the PABX systems of most major countries. The high level of programmability allows the SA9401 to satisfy a wide variety of tone plans. Furthermore by providing three inputs to select between one of eight tone programs during initialisation, the device effectively facilitates the design of a universally programmable "PABX Processor Card". Because the tone program inputs are latched at the start of each PCM frame the SA9401 minimises the possibility of glitches. The SA9401 can also generate the PCM Frame synchronising reference signal if required.