Multiple Key Closures - Motorola Freescale Semiconductor M-Core MMC2001 Reference Manual

Keypad
NAND
Matrix
. . .
Figure 14-6 Keypad Synchronizer Functional Diagram

14.4.6 Multiple Key Closures

One or two keys pressed simultaneously are easily detected by the software. When
three or more keys are pressed, however, it is possible that errant key closures may
be detected. As can be seen in Figure 14-7, three keys pressed simultaneously can
short between the column currently "scanned" by software and another column.
Depending on the location of the third key pressed, a "ghost" key press may be
detected.
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14-8
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D Q
FF
S
Set KPKR Synchronizer
D Q
FF D Q
R
256 Hz
Clear KPKD Synchronizer
KEYPAD PORT
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D Q
FF
D Q
S
FF
D Q
S
FF
Clear KPKR Status Flag
FF
D Q
R
FF
D Q
R
FF
R
Clear KPKD Status Flag
S
KPKR
^S
R
KPKD
^S
R
MMC2001
REFERENCE MANUAL