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Standard Microsystems/SMC

SMC, variously known as Standard Microsystems Corporation or SMC Microsystems Corporation, later SMSC. SMSC was bought by Microchip, while SMC Networks may still exist.


Keyboard encoder ICs

Families KR2376 and KR3600 were either second-sourced or cloned from, or second-sourced or cloned as the equivalent chips from General Instrument. KR2376 and KR3600 could both be found in the Data Catalog 1979 through 1982 (see SMC catalogues). By 1985, KR2376 was no longer listed, and KR9600, KR9601 and KR906 had appeared. In the Data Catalog 1986, KR3600 was no longer listed, having been replaced with KR9600.

A Tatung TPC-2000 keyboard has been found with a keyboard encoder marked “SMC 8426C”. In the documentation, the encoder is a National Semiconductor MM57499, for which 8426C may be a compatible part. There seems to be no acknowledgement of the existence of a model 8426C or KR8426.

Model Keys Modes Bits/key Rollover Output Data Notes
KR2376 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, 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)
Direct replacement for the KR3600
KR9602 Serial Binary sequential (KR9602-STD)
ASCII (KR9602-012)


The oldest discovered KR2376 example is a KR2376-17 from a DEC VT05, dated from week 52 1973. This type appears to be in a ceramic package, rather than the more common plastic package.

Part number Purpose
KR2376-ST Selcom/Jen Lemon II
KR2376-012 George Risk model 753 keyboard, as well as the model 771; Netronics ELF II
KR2376-17 Digital Equipment VT05
KR2376-150 Used by Carter Keyboards models 756, 771 and 777 (and maybe others); these appear to be George Risk keyboards also, although the official 771 schematic shows a KR2376-012


KR3600 was available in both mask-programmed and ROMless (binary sequential) forms. KR3600-PRO is the ROMless version: this model can be used together with an external ROM containing the look-up table of character codes, or the conversion from matrix position to character code or key identity can be performed in the operating system. The mask-programmed models used a suffix to indicate what mask was used. For customer-specific models, this suffix was a numeric code. SMC also provided two standard programmed models, KR3600-STD and KR3600-ST. The product literature does not explain or differentiate these two variants. KR3600-ST provides standard ASCII mapping along with variants. For example, question mark can be either on a [? <] key or on a standard [/ ?] key. Keys 0–9 are defined twice: once with conventional shift, control and shift+control modes, and separately where control and shift have no effect (perhaps for use with a numeric keypad where the customer feels that shift and control should not affect the output). KR3600-STD has a very peculiar mapping; for example, SOH is control+1 instead of the expected control+A, and control+shift+A produces @.

The following usage is known:

Part number Purpose
KR3600-PRO ROMless version, to be used in conjunction with an external ROM
KR3600-STD Strange ASCII mapping
KR3600-ST Standard ASCII mapping
KR3600-056 Superbrain
Apple II Europlus (Apple part 331-0931-B)
KR3600-075B1 Apple II and III (Apple part 341-0035-A and 342-0035)

The following models have been encountered, typically as surplus parts; their assignments are not known: KR3600-080, KR3600-153, KR3600-154. Various other numbers can be found via an Internet search, all likely to be genuine SMC parts.

KR9600, KR9601, KR9602

KR9600 is a direct replacement for KR3600 that removes the need for a separate −12 V power input. KR3600 has two power inputs: +5 V VCC on pin 30 and −12 V VGG on pin 27. The need for −12 V was an awkward requirement of various encoders, and on KR9600 pin 27 is left unconnected, with a single 5 volt supply being sufficient for all functionality.

KR9600 is a drop-in replacement for KR3600 (although the NKRO diode polarity must be reversed) while KR9601 is an improved model with a slightly different pinout. KR9601 and KR9602 implement a dedicated caps lock feature (separate from shift lock) which makes use of the spare pin 27 released by removing the −12 V power input; they also implement auto-repeat.

KR9600 and KR9601 are parallel encoders in DIP-40 packages. KR9602 is the serial equivalent to KR9601, and fits into a smaller DIP-28 package. KR9600 and KR9601 are designed for internal keyboards connected to the motherboard via a parallel cable, while KR9602 is designed for external keyboards connected via a serial cable. The DIP-40 models also have configuration pins: six on KR9601, and five on KR9600, as pin 6 on KR9600 is the 9th data output bit.


The following datasheets cover SMC keyboard encoder ICs:

The following material was scanned by Bitsavers: