LG -A290 Service Manual page 50

3. TECHNICAL BRIEF
This keypad can detect one or two key-pressed simultaneously with any combination. Figure 3.1.3 shows one key
pressed condition. Figure 3.1.4(a) and Figure 3.1.4(b) illustrate two keys pressed cases. Since the key press detection
depends on the HIGH or LOW level of the external keypad interface, if keys are pressed at the same time and there exists
a key that is on the same column and the same row with the other keys, the pressed key cannot be correctly decoded.
For example, if there are three key presses: key1 = (x1, y1), key = (x, y), and key3 = (x1, y), then both key3 and key4
= (x, y1) are detected, and therefore they cannot be distinguished correctly. Hence, the keypad can detect only one or
two keys pressed simultaneously at any combination. More than two keys pressed simultaneously in a specific pattern
retrieve the wrong information.
Figure 3.12.3 One key pressed with de-bounce mechanism denoted
Figure 3.12.4 Two keys pressed, case 1 (b) Two keys pressed, case 2
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