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Keyboard encoder ICs

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LSI encoder circuits

The following table lists known keyboard encoder integrated circuits. These are LSI implementations that do not involve the use of a microprocessor. See encoding and output for more details on keyboard encoding.

The datasheets are often not clear on the distinctions between the different models, and only brief details are given here at the moment.

Model Manufacturer Keys Modes Bits/key Rollover Output Data Notes
AY-5-2376 General Instrument 88 3 9 2KRO/N-key lockout Parallel ASCII, custom 11×8 matrix; 88 keys × 3 modes/key × 9 bits/mode/key = 2376 bits of ROM; by default, the 9th bit is used for parity
AY-3-4592 112 4 10 2KRO/NKRO Parallel 16×8 matrix using an external multiplexer; supports “capacitive, magnetic, inductive, Hall effect [and] mechanical” switches using pulse detection; 2KRO/NKRO is dynamically selectable; ROM size is 4592 bits; 128-key matrix with 112 encoded keys plus 16 discrete function keys
AY-5-3600 90 4 9 NKRO/N-key lockout Parallel ASCII (AY-5-3600)
Binary sequential (AY-5-3600-PRO)
9×10 matrix; 90 keys × 4 modes/key × 9 bits/mode/key = 3600 bits of ROM
MM5740 National Semiconductor 90 4 9 2KRO/NKRO Parallel ASR-33 NKRO (MM5740AAE)
ASR-33 2KRO (MM5740AAF)
9×10 matrix; bits 0–4 and 8 are common to all modes
MM5745 78 4 10 2KRO/NKRO Parallel Custom 2-of-13 input (non-matrix); listed as 2KRO/NKRO but no explanation is given regarding how NKRO works without matrix scanning
MM5746 9
MM57499 96/144 3 8 2-key lockout Serial ASCII and special codes 96 keys natively (12×8 matrix), and 144 keys with an external decoder (12×12 matrix); serial input permits output passthrough or eight bits of status display
KR2376-XX SMC 88 3 9 2KRO/N-key lockout Parallel ASCII, custom Possibly a substitute for AY-5-2376
KR3600 90 4 10 NKRO/N-key lockout Parallel Custom (KR3600-XX)
ASCII (KR3600-ST)
ASCII, NKRO-only (KR3600-STD)
Binary sequential (KR3600-PRO)
Pin-for-pin replacement for GI AY-5-3600
KR9600 90 4 10 NKRO/N-key lockout Parallel Binary sequential (KR9600-PRO)
ASCII (KR9600-STD)
Direct replacement for the KR3600
KR9601 ASCII
KR9602 Serial Binary sequential (KR9602-STD)
ASCII (KR9602-012)