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A peripheral interface unit for a microcomputer control system fabricated by a standard n-channel silicon-gate enhancement/ depletion MOS process is described. This unit can accept analog and digital inputs, generate pulse outputs, and multiply. The analog input capability is made possible by an on-chip A/D converter using a constant slope approach with an external capacitor. This converter can perform a 10 bit conversion in 5 ms and has an input voltage range of 0-5 V with only one 8 V power supply for the analog circuits. The die area required by the converter is small and the precision analog specifications needed for the process and devices are few. The die area of the converter is 3 mm2, out of a total unit area of 35 mm2.