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Microprocessor Controlled Keyboard Scan Technique

IP.com Disclosure Number: IPCOM000049404D
Original Publication Date: 1982-Apr-01
Included in the Prior Art Database: 2005-Feb-09
Document File: 2 page(s) / 31K

Publishing Venue

IBM

Related People

Rowe, JT: AUTHOR

Abstract

Many microprocessor-controlled keyboards exist. Microprocessors for applying scanning pulses to a key matrix are similarly well known. The state of the art normally employs one or two scanning pulses to detect and verify the depression or release of a key. In this known technique, two or three sequential drive pulses must be detected before a decision that a key depression or release has occurred will be decoded.

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Microprocessor Controlled Keyboard Scan Technique

Many microprocessor-controlled keyboards exist. Microprocessors for applying scanning pulses to a key matrix are similarly well known. The state of the art normally employs one or two scanning pulses to detect and verify the depression or release of a key. In this known technique, two or three sequential drive pulses must be detected before a decision that a key depression or release has occurred will be decoded.

These techniques are subject to interference and noise which may masquerade as sensing pulses or which may mask the detection of them. The 3- pulse scheme shown in the figure requires longer bursts of noise to affect all three pulses and hence provides a higher degree of security in sensing.

A further modification, as shown, is the delaying of the third scanning pulse. This has the effect of increasing the duration of noise required to affect all three pulses and also increasing the frequency or repetition rate of noise spikes that would be necessary in order to interfere with the scanning. By delaying the third scan pulse, the third pulse is made to be out of synchronization with any noise affecting the first two pulses. In order to affect all three pulses, the periodicity of the noise must be equal to a common multiplicative factor of both the duration between the first and second drive pulses and the duration between the second and third pulses, as shown in the diagram. The use of the delay pulse moves...