Cirrus Logic EP93xx - Manual (Page 765)

DS785UM1 26-3
Copyright 2007 Cirrus Logic
Keypad Interface
EP93xx User’s Guide
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Figure 26-2. 8 x 8 Key Array Diagram
26.2.1 Apparent Key Detection
When more than two keys are pressed, the key array controller may detect “apparent” keys.
An apparent key detection is caused by misinterpreting the basic electrical signals. For
example, in
Figure 26-3 , three keys are pressed:
• (ROW0, COL3) with address 0x03
• (ROW3, COL0) with address 0x18
• (ROW3, COL3) with address 0x1B
The controller’s instruction is to decode the two keys with the lowest addresses. Therefore
the system interprets the electrical signals as:
• An apparent key address of 0x00 at (ROW0, COL0)]
• An actual key address of 0x03 at (ROW0, COL3)
• No press for address 0x18 at (ROW3, COL0)
ROW 0
KEY 00H KEY 01H KEY 02H KEY 03H KEY 04H KEY 05H KEY 06H KEY 07H
ROW 1
KEY 08H KEY 09H KEY 0AH KEY 0BH KEY 0CH KEY 0DH KEY 0EH KEY 1FH
ROW 2
KEY 10H KEY 11H KEY 12H KEY 13H KEY 14H KEY 15H KEY 16H KEY 17H
ROW 3
KEY 18H KEY 19H KEY 1AH KEY 1BH KEY 1CH KEY 1DH KEY 1EH KEY 1FH
ROW 4
KEY 20H KEY 21H KEY 22H KEY 23H KEY 24H KEY 25H KEY 26H KEY 27H
ROW 5
KEY 28H KEY 29H KEY 2AH KEY 2BH KEY 2CH KEY 2DH KEY 2EH KEY 2FH
ROW 6
KEY 30H KEY 31H KEY 32H KEY 33H KEY 34H KEY 35H KEY 36H KEY 37H
ROW 7
KEY 38H KEY 39H KEY 3AH KEY 3BH KEY 3CH KEY 3DH KEY 3EH KEY 3FH
COL 0 COL 1 COL 2 COL 3 COL 4 COL 5 COL 6 COL 7