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RCA single-chip keyboard encoders

Contents

Models

RCA are known to have produced at least one model of single-chip keyboard encoder, CDP1871.

RCA also filed a patent in 1971, granted in 1973 as US patent 3778815 “Keyboard encoder”, for an encoder for a hexadecimal keypad. Whether this was implemented as a single chip or with discrete parts is not known.

CDP1871

CDP1871 is an ASCII-only encoder with no ROM and thus no provision for customisation. CDP1871 was designed to be used with the CDP1800-series microprocessor. The output of each key is determined by its matrix position in conjunction with the state of the control, shift and alpha lock keys. Alpha lock is expected to use an alternate action switch.

The encoder is quad-mode (normal, shift, control and alpha lock) and provides support for 85 keys via an 11×8 matrix. Matrix positions (7, 2), (7, 5) and (7, 7) are not operational. Matrix positions (1, 8) through (7, 8) produce ASCII output across 53 keys. The remaining four columns 8–11 output the 32 characters in the range 0x80–0x9F.

The control key is stated to override the shift and alpha lock keys.

Ownership of the product passed to Harris Semiconductor after the latter acquired RCA’s semiconductor division, and in turn passed to Intersil after Harris divested its semiconductor operations. The CDP1871A/CDP1871AC datasheet can be found both with Harris and with Intersil branding.

The earliest-discovered reference to CDP1871 is in a CMOS components advertisement in Electronics magazine in October 1979, where it is one of the parts listed as “coming soon”. In RCA’s 1982 CMOS LSI Microprocessors, Memories, Peripherals databook, the entry for CDP1871A/CDP1871AC is marked “Preliminary Data”. Even by the 1984 edition, the CDP1871A/CDP1871AC is marked “Advance Information/Preliminary Data”. By the time of the unidentified catalogue entry below, the specifications had been finalised.

Documentation