Keyboard with N-key lockout and two-key rollover protection

Details Keyboard with N-key lockout and two-key rollover protection Keyboard with N-key lockout and two-key rollover protection

1975-07-15

1976-08-31

Habecker, Thomas B.

Communications: electrical

Audible indication

Percussion-type sound producer

340174PM, G08C 2500

Patent

active

039784746

ABSTRACT:
A keyboard having N-Key Lockout and Two-Key Rollover Protection is disclosed. Each key switch of the keyboard is assigned a unique time slot in a scan cycle. A key switch actuation results in a logic "1" signal at the input of a shift register which is shifted to the output of the shift register one scan time later. Comparison of the input and output states of the shift register results in a signal which indicates when any key switch has not been actuated during the last scan cycle in order to reset a flip-flop which produces a strobe pulse to external data processing equipment. A modulus 2 counter, and other associated circuitry, inhibits the strobe pulse whenever two key switches are actuated during the same scan cycle.

REFERENCES:
patent: 3816826 (1974-06-01), Masuda
patent: 3918051 (1975-11-01), Bernin

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