Design of a Memory Controlled PCM System

Abstract

Airborne PCM Telemeters are essentially alike in that they multiplex digital and analog data from numerous sources and format it into a serial data stream. Because of radical format differences in data requirements, however, frequent redesign of format generation logic is mandatory. The recent development of small non-volatile Read Only Memories with large bit capacities has suggested a telemeter whose characteristics can be altered merely by replacing a memory. The authors solution to the problem of the "universal encoder" is the design of the MPS-101 whose word format is controlled by a MOS-FET Read Only Memory. The MPS-101 can store six reasonably complex formats in its 6144 bit plug-in memory card. To insure flexibility, a bit rate oscillator and a premodulation filter are included within the interchangeable module. A program plug enables the user to address (select) the desired format, control the word size, select parity and vary the bit rate. Data rates can be clocked up to 750 KB/S, with no effect on system accuracy. This work has resulted in an encoder whose format is totally arbitrary and whose data structuring and major/minor frame synchronization techniques are strictly under "software" control. This work was performed under Sandia Laboratories Contract Number 72-3233.