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JE610 ASCII Keyboard Encoder

JE610 is a complete keyboard kit supplied by Jameco, based around a Hi-Tek “High Profile” switch array and a General Instrument AY-5-2376 LSI keyboard encoder. Due to limitations of the AY-5-2376, two significant features of this keyboard are implemented in additional TTL: the Repeat key, and Caps Lock. The AY-5-2376 has support for both Control and Shift keys (and by extension, Shift Lock) but Caps Lock requires more complex circuitry to only apply bit manipulation to the A-Z keys. Thus, the Caps Lock key (which is implied from the circuit diagram to be alternate action) is supported by a special circuitry that adjusts the output codes as applicable. Support for both positive-going and negative-going strobe is provided separately by splitting the strobe output and feeding one of the two lines through a NAND gate to invert it.

The use of a dedicated encoder does reduce the total chip count to only seven. The IC descriptions in the documentation are vague and in one case incorrect (the hex inverter is described as a hex buffer); the complete list of ICs is as follows:

Part Function Qty
AY-5-2376 88-key tri-mode keyboard encoder, parallel output with parity 1
74LS02 Quad 2-input NOR gate 1
74LS00 Quad 2-input NAND gate 1
7425 Dual 4-input NOR gate with strobe 1
556 Dual timer 1
74LS05 Hex inverter 2

There is also a JE610 with a Stackpole KS-200 array, suggesting that Jameco may have sourced the key arrays from both Stackpole and Hi-Tek.