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BU1851GUW bảng dữ liệu(PDF) 9 Page - Rohm |
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BU1851GUW bảng dữ liệu(HTML) 9 Page - Rohm |
9 / 13 page Technical Note 9/12 BU1851GUW www.rohm.com 2009.09 - Rev.A © 2009 ROHM Co., Ltd. All rights reserved. 4. Ghost Key Rejection Ghost key is an inevitable phenomenon as long as key-switch matrices are used. When three switches located at the corners of a certain matrix rectangle are pressed simultaneously, the switch that is located at the last corner of the rectangle (the ghost key) also appears to be pressed, even though the last key is not pressed. This occurs because the ghost key switch is electrically shorted by the combination of the other three switches (Fig.7). Because the key appears to be pressed electrically, it is impossible to distinguish which key is the ghost key and which key is pressed. The BU1851 solves the ghost key problem to use the simple method. If BU1851 detects any three-key combination that generates a fourth ghost key, and BU1851 does not report anything, indicating the ghost keys are ignored. This means that many combinations of three keys are also ignored when pressed at the same time. Applications requiring three-key combinations (such as <Ctrl><Alt><Del>) must ensure that the three keys are not wired in positions that define the vertices of a rectangle (Fig. 8). There is no limit on the number of keys that can be pressed simultaneously as long as the keys do not generate ghost key events. Fig.7 Ghost key phenomenon Fig.8 Valid three key combinations GHOST-KEY EVENT PRESSED KEY EVENT KEY-SWITCH MATRIX KEY-SWITCH MATRIX KEY-SWITCH MATRIX EXAMPLES OF VALID THREE-KEY COMBINATIONS |
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