US 4,617,554 AGranted

Keyboard scanning

AssigneeZenith Electronics Corporation

InventorsCharles A. Krause, Randy J. Vander Heyden

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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.

Claims11

Dependent claims

In a matrix-type keyboard having a plurality of selectively engageable keys representing a plurality of alphanumeric characters and operating modes and signal processing means including memory means having a plurality of locations for the detection and storage of engaged key information therein, a method for detecting the simultaneous engagement of more than one of said keys comprising:

sequentially generating a plurality of first scan signals and providing said scan signals to said keyboard for the sequential scan thereof;
detecting a first output scan signal from said keyboard representing the engagement of a first alphanumeric character key therein;
storing said first output scan signal in a first location in said memory means;
sequentially generating a plurality of second input scan signals and providing said scan signals to said keyboard for the sequential scan thereof;
detecting a second output scan signal from said keyboard representing a second alphanumeric character key engaged simultaneously with said first key;
storing said second output scan signal in a second location in said memory means;
detecting the deselection of said first key or said second key;
storing said second output scan signal in said first memory location if said first key has been deselected;
detecting the engagement of a key representing an operating mode following the selection of said second key;
sequentially generating a plurality of third input scan signals and providing said scan signals to said keyboard for the sequential scan thereof;
detecting a third output scan signal from said keyboard representing the engagement of a third alphanumeric character key therein;
and
storing said third output scan signal in said second location in said memory means.

10 more elements

A system for detecting the simultaneous engagement of more than one key in a matrix-type keyboard having a plurality of selectively engageable keys representing a plurality of alphanumeric characters and operating modes, wherein said keyboard provides an output signal representing the selection of a given key, said system comprising:

signal generating means coupled to said keyboard for generating first and second pluralities of scan signals for sequentially scanning said keyboard;
signal processing means coupled to said keyboard for simultaneously receiving first and second output signals from said keyboard representing the selection of first and second alphanumeric character keys engaged at the same time, wherein said first key is selected first;
memory means coupled to said signal processing means and including first and second memory locations for storing said first and second output signals, wherein said first output signal is initially stored in said first memory location and is subsequently stored in said second memory location following the detection and storage of said second output signal in said first memory location;
key detection means coupled to said keyboard for detecting the deselection of said first or second keys;
means for detecting the engagement of an operating mode key following the engagement of said second key;
and
data transfer means coupled to said key detection means and said memory means and responsive to the deselection of said first key for transferring said second output signal to said first memory location following the deselection of said first key, wherein a third output signal representing the engagement of a third alphanumeric character key generated in response to a third plurality of scan signals provided by said signal generating means to said keyboard is stored in said first memory location.

4 more elements

Dependencies are inferred from the claim text.