Keyboard scanning

Details Keyboard scanning Keyboard scanning

1983-08-26

1986-10-14

Caldwell, Sr., John W.

Communications: electrical

Audible indication

Percussion-type sound producer

340365R, G11C 1900

Patent

active

046175547

ABSTRACT:
A multi-key keyboard is scanned at high speed in such a manner as to substantially reduce erroneous key entries caused by the simultaneous engagement of more than one key. A keyboard processor determines which key is down by sequential scanning of the keyboard, encodes the selected key and sends this code to a master processor, or CPU. A 2-key lockout scanning approach is employed wherein keyboard scanning stops when two keys are selected simultaneously. Scanning is resumed when either one or both of the first two keys are released. By limiting simultaneous key engagement detection to two keys, system complexity and cost are kept within reasonable limits while insuring against erroneous key entries. Detecting and storing the key engagement sequence permits a selected special function, e.g., automatic key repeat, to be applied to the last selected key rather than to an earlier selected, but simultaneously engaged, key.

REFERENCES:
patent: 4106011 (1978-08-01), Melanson et al.

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