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General Instrument keyboard encoders



General Instrument produced both MOS/LSI keyboard encoders as well as microprocessor-based keyboard encoders. Families AY-5-2376 and AY-5-3600 were either second-sourced to, or cloned by, Standard Microsystems.


The following table lists just the MOS/LSI encoders:

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 was advertised as far back as September 1971 in the Electronic Engineer magazine. It was also mentioned in US patent 3974575 “Teaching machine”, filed in June 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-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.

The Apple II/II+ Level II Service Manual indicates that the keyboard encoder in most Apple II keyboards (aside from the early Datanetics keyboards which used a National Semiconductor MM5740) is part number AY-5-3600-931, where 931 is presumably the customisation code. This chip can be seen in the Applefritter forum topic Apple II Plus keyboard - strange output on Mimeo, where it is labelled simply “NKBD-931” (attachment “encoder board.jpg”).

A chip marked “AY-5-3600-PRO” and “PRO-050” can be seen in an Omnidata Omni 1 keyboard. The US-made Omni 1 keyboard is almost identical to the German-made Cherry G80-0115 which uses instead an SMC KR3600-PRO. The same “PRO-050” designation can be seen on an AY-5-3600-PRO used in an Apple ][ clone keyboard.

A failed AY-5-3600-PRO can be replaced by Joe’s Computer Museum’s JCM Universal Keyboard Encoder. Joe’s Computer Museum also offers customised versions as a service for those who need to replace a chip with ASCII output or custom programming.


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.

KB3600 and KB3600-PRO

KB3600 is a microprocessor-based encoder. KB3600 features N-key rollover, 9-bit output codes and a 5.4 ms debounce time. Separate ASCII (KB3600) and binary sequential (KB3600-PRO) models were offered, and custom output table configuration was available. KB3600 was advertised in Computer Design magazine in September 1983. In quantities of 25,000 these encoders sold for $2.30 each, or $6.10 in April 2021 prices.

While most companies used variants of Intel’s MCS-48 and MCS-51 microcontrollers with mask-programmed encoder firmware, General Instrument built the KB3600 around their own PIC1650A microcontroller (itself the original product that begot the Microchip PIC family). KB3600 is so named because it is programmed to behave identically to the AY-5-3600. Although KB3600 is a custom product from General Instrument, the pinout of the chip differs from that of AY-5-3600, and as such they are not interchangeable. The options pins from the AY-5-3600 are also missing; N-key rollover vs N-key lockout is still configurable, but now only via mask programming.

Custom models

General Instrument also provided custom encoders for their Clare-Pendar subsidiary, starting from around 1970.

Part number Date Keyboard
S077D-6 7114 Clare-Pendar 700610-K15 (PDF page 14)
78372C-007 7345 Clare-Pendar K353

S077D-6 is listed on eBay, and the chip is virtually identical to the one in Clare-Pendar’s 1970 MOS keyboards NOW! in the, July 19 1970 issue of Electronic Design magazine. (The chip in the advertisement is however entirely unmarked.)


The following material was scanned by Bitsavers unless otherwise noted.


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