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Abstract

An electronic musical instrument includes a programmed microprocessor for controlling selected functions of the instrument and a plurality of key and tab switches responsive to a scan control signal repetitively scanning the switches for developing a serial data signal defining operated key and tab switches during each of the scans. An interface circuit is interposed between the key and tab switches and the microprocessor for developing the scan control signal and for receiving the resulting serial data signal. The serial interface circuit includes means for converting the received serial data into a number of first multibit words each representing a depressed key and a number of second multibit words each bit of which represents the operational condition of a respective one of the tab switches. The first and second multibit words are stored in a RAM in a compressed format, the RAM being enabled for coupling its contents in parallel form to the microprocessor in response to two consecutive scans of the key and tab switches resulting in the development of identical serial data signals immediately preceded by a scan resulting in the development of a serial data signal different therefrom. The interface circuit also includes means for converting data words coupled to the RAM from the microprocessor into a corresponding serial data output signal.

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