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Keyboard Membrane Structure for Shift Keys

IP.com Disclosure Number: IPCOM000035297D
Original Publication Date: 1989-Jul-01
Included in the Prior Art Database: 2005-Jan-28
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Anderson, FE: AUTHOR [+2]

Abstract

This article describes the keyboard membrane for typewriter and PC products modified to eliminate the "beat the shift" problem. In one aspect of this problem, the typing keys as well as the shift keys are tied into a matrix of drive lines and sense lines, and this matrix is periodically scanned to see which keys are activated, and at some time during the scan the shift key activation is scanned. This latter scanning may come before or after the scanning of the condition of the activation of the character key. In the case of a very rapid typist, this typist may have released the shift key after striking the character key, but before the condition of the shift key has been sensed. This will cause the wrong character mode (cap or non-cap) to be typed.

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Keyboard Membrane Structure for Shift Keys

This article describes the keyboard membrane for typewriter and PC products modified to eliminate the "beat the shift" problem. In one aspect of this problem, the typing keys as well as the shift keys are tied into a matrix of drive lines and sense lines, and this matrix is periodically scanned to see which keys are activated, and at some time during the scan the shift key activation is scanned. This latter scanning may come before or after the scanning of the condition of the activation of the character key. In the case of a very rapid typist, this typist may have released the shift key after striking the character key, but before the condition of the shift key has been sensed. This will cause the wrong character mode (cap or non-cap) to be typed. According to this invention, a new sense line is added with only the right and left shift keys tied to it. The drive is provided by a ground connection since this is a dedicated sense line. A small value of resistor and capacitor on the sense drive provides the debounce with the new line going to the scan control logic. The scan control logic reads the new sense line state when any key is debounced attaching a shift bit as the make/break bit is currently attached.

This system assigns a shift value to any debounced key such that the current millisecond delays in detecting the shift state are eliminated since the shift line is always active and this is sensed concomitantly with...