A MOS LSI capacitive keyboard interface chip

A single chip silicon gate LSI device is described which interfaces a microprocessor to a capacitive keyboard. The LSI circuit replaces a large number of MSI devices and substitutes a unique digital key detection scheme for the more traditional differential amplifiers. On chip are an internal oscillator, a clock generator, key matrix scanning and detection circuits, a digital filter, input sensing circuits with hysteresis, multiple key rollover electronics, and handshaking logic to interface asynchronously with any standard 8-bit microprocessor such as the 8080. Off chip is only an RC network for the purpose of setting the oscillator frequency.