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The Bendix Corporation was an American manufacturer.


NASA keyboard

Bendix are known for manufacturing a control panel for NASA incorporating a keyboard. This NASA control panel, from Bendix’s Flight Systems Division, uses Clare-Pendar S84020 double-pole mechanical switches. From additional photos from its owner, the inventory of ICs in the keyboard portion of the unit can be seen to be as follows:

Model Qty Description
5400 3 Quad 2-input NAND gate
5404 1 Hex inverter
5432 1 Quad 2-input OR gate
5474 1 Dual D positive edge triggered flip-flop, asynchronous preset and clear
54121 1 Monostable multivibrator (Schmitt trigger input)
54123 1 Dual retriggerable monostable multivibrator, clear
54128 3 Quad 2-input NOR gate (driver 50 Ω)
9318 4 8-input priority encoder
PROM1 2 1024-bit PROM

All the ICs are military grade: 5400 series is ceramic-encased military equivalent of 7400-series. The four AMD 9318DM chips are also military grade, with D denoting ceramic packaging and M denoting military grade. Most of the ICs were sourced from Signetics; Texas Instruments provided the SN5432J, while AMD provided the binary encoders. The two PROMs are of uncertain origin, not quite matching either Harris or Honeywell markings.

With component dates from 1973 and 1974, final assembly was likely performed in 1974.

The roster of ICs lacks any method of tracking matrix co-ordinates, and the two outputs from each switch are wired up entirely separately instead of for redundancy. Combined with the existence of a full four binary encoders, all evidence points to this keyboard being two-of-N encoded. Instead of a encoding grid, it appears that conversion from key identity to output code is provided by 2048 bits of ROM (in two 1024-bit PROMs); this precise quantity of storage provides for a full 256 keys (the limit of the four binary encoders) to have a single output code each. Whether shift is handled on-keyboard or by the host is left to someone who can trace the circuit and the logic.

One interesting mystery remains: since there is no sign of an electrical monitor detector, what method is used to detect keystroke clashes?