Microcomputer interfaced electronic organ

A microcomputer interfaced electronic musical instrument comprising:

• a keyboard having a plurality of keyswitches,
• multiplexer means for continuously and cyclically scanning said keyswitches and producing a time division multiplexed data stream comprising a plurality of time slots corresponding to respective ones of said keyswitches and keydown signals in time slots corresponding to actuated said keyswitches,
• assignment control means having an input connected to said data stream for monitoring said data stream and producing a multiple bit key actuated word when a keydown signal newly appears in a time slot which previously did not contain a keydown signal and for producing a multiple bit key released word when a keydown signal disappears from a time slot that previously contained a keydown signal, said key actuated and key released words being coded to identify the time slots in which the respective keydown signals newly appear and disappear,
• programmable microcomputer means connected to said assignment control means for sequentially accepting and operating on the key actuated and key released words produced by said assignment control means and producing on an output digital tone generator-keyer assignment words containing keydown, key release, and tone frequency and amplitude envelope information, said microcomputer means accepting key actuated and key released words from said assignment control means at a rate slower than the rate at which the keyswitches are scanned by said multiplexer means,
• a plurality of tone generator-keyer means each capable of producing and keying a tone having a selectable frequency and an attack and decay amplitude envelope,
• register control means interposed between said microcomputer means output and said plurality of tone generator-keyer means for steering the tone generator assignment words to selected tone generator-keyer means in accordance with instructions from said microcomputer means,
• said tone generator-keyer means being responsive to said information in the assignment words to produce tones having corresponding frequencies and amplitude envelopes,
• said assignment control means including means for comparing the data stream from said multiplexer means with data for each time slot corresponding to whether the last word transmitted to said microcomputer means for that time slot was a key depressed word and for causing a key actuated word to be transmitted to said microcomputer means when a keydown signal appears in the time slot for which the last word transmitted to said microcomputer means was not a key actuated word and for causing a key released word to be transmitted to said microcomputer means when no keydown signal appears in a time slot for which the last word transmitted to said microcomputer means was a key actuated word;
• and
• said microcomputer means including means for transmitting to said assignment control means keyer busy data indicating that no tone generator-keyer means are available for a particular group of keyswitches and said assignment control means includes means responsive to said keyer busy data for inhibiting the transmission to said microcomputer means of a key actuated word for one of that particular group of keyswitches.