Key detection system interconnecting keyboard and data processing system
First Claim
1. In a data processing system including a central processing unit and a peripheral device having a keyboard through which an operator may key in data by momentarily closing key contacts of individual keys as they are depressed, apparatus for coupling said keyboard to said central processing unit comprisingmeans for continually scanning said contacts of individual keys of said keyboard in search of closed contacts indicating a key has been depressed,means for storing a unique code representative of a key found depressed during a given scanning cycle following at least a predetermined number of scanning cycles during which no depressed key is found,means for comparing a unique code representative of a key found depressed during each scanning cycle following said given scanning cycle,counting means responsive to said comparing means for counting up each cycle that the unique code of a key found corresponds to the unique code stored in said storing means up to said predetermined number of cycles and maintaining said number as a maximum count so long as the key found continues to correspond, and for counting down each cycle that no key is found depressed or that the unique code of a key found does not correspond to the unique code stored in said storing means, andmeans responsive to said counting means for initiating transfer of said unique code to said central processing unit when said predetermined number is reached as a maximum count.
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Abstract
A system is disclosed for scanning a keyboard and detecting any depressed key during each scan cycle, and for filtering out any bounce in key contacts closing and opening with a filtering up-down counter that counts up each scan cycle that the same key is found, down each cycle that a different key is also found or that no key is found, and requiring that the filtering counter reach a selected maximum before finding that a key is depressed and that the filtering counter reach zero before starting to filter another key detected to be depressed.
28 Citations
10 Claims
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1. In a data processing system including a central processing unit and a peripheral device having a keyboard through which an operator may key in data by momentarily closing key contacts of individual keys as they are depressed, apparatus for coupling said keyboard to said central processing unit comprising
means for continually scanning said contacts of individual keys of said keyboard in search of closed contacts indicating a key has been depressed, means for storing a unique code representative of a key found depressed during a given scanning cycle following at least a predetermined number of scanning cycles during which no depressed key is found, means for comparing a unique code representative of a key found depressed during each scanning cycle following said given scanning cycle, counting means responsive to said comparing means for counting up each cycle that the unique code of a key found corresponds to the unique code stored in said storing means up to said predetermined number of cycles and maintaining said number as a maximum count so long as the key found continues to correspond, and for counting down each cycle that no key is found depressed or that the unique code of a key found does not correspond to the unique code stored in said storing means, and means responsive to said counting means for initiating transfer of said unique code to said central processing unit when said predetermined number is reached as a maximum count.
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5. Apparatus for automatically scanning a keyboard for the purpose of detecting depressed keys in the order depressed and presenting a key identifying code to a data processing system without double detection and identification of a single depressed key due to bouncing key contacts, comprising
means for automatically and cyclically scanning all key contacts in search of closed key contacts and for identifying each with a unique key code corresponding to the position in the scan cycle that key contacts are detected closed, means for signalling to said data processor when a depressed key has been found and identified, and means for filtering out any bounce in key contacts closing before actuating said signalling means upon a key being depressed including means for counting up to a predetermined number of scan cycles the same key contacts are detected closed and counting down each scan cycle the same key contacts are not detected closed before actuating said signalling means.
Specification