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General Instrument

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Keyboard encoder ICs

Families AY-5-2376 and AY-5-3600 were either second-sourced to, or cloned by, SMC.

Model Keys Modes Bits/key Rollover Output Data
AY-5-2376 88 3 9 2KRO/N-key lockout Parallel ASCII, custom
AY-3-4592 112 4 10 2KRO/NKRO Parallel
AY-5-3600 90 4 9 NKRO/N-key lockout Parallel ASCII
AY-5-3600-PRO Binary sequential

AY-5-2376

AY-5-2376 is mentioned in US patent 3974575 “Teaching machine”, indicating that this model was available by 1974.

AY-5-2376 uses an 11×8 matrix. 88 keys × 3 modes/key × 9 bits/mode/key = 2376 bits of ROM, whence the model number. By default, the 9th bit is used for parity

AY-3-4592

AY-3-4592 supports “capacitive, magnetic, inductive, Hall effect [and] mechanical” switches using pulse detection. The encoder provides a 128-key matrix with 112 encoded keys and 16 discrete function keys. It addresses a 16×8 matrix using an external multiplexer. 2KRO/NKRO is dynamically selectable. The ROM size is 4592 bits.

AY-5-3600 and AY-5-3600-PRO

Model AY-5-3600 is a 90-key quad-mode encoder. Each key generates a 9-bit code per mode, for a total of 3600 bits of ROM providing the key definitions. The standard model generates ASCII output. The matrix size is 9 × 10.

Where the manufacturer needs to provide a different set of output codes, model AY-5-3600-PRO is used. This outputs only the scancodes, with the intention being that the output codes be used as the indexes into a PROM or EPROM containing the character definitions.

Documentation

The following documents cover General Instrument keyboard encoder ICs: