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Pulled Down Row
Pulled Down Row
The path of the zero pull down
that reaches the wrong row and so
generates a ghost key press
Figure 14-7 Decoding Wrong Three Key Presses
14.4.7 Typical Keypad Configuration and Scanning Sequence
1. Configure keypad
a. Enable number of rows in keypad (KPCR[7:0]).
b. Write zeros to KPDR[15:8].
c. Configure keypad columns as open-drain (KPCR[15:8]).
d. Configure columns as output, rows as input (KDDR[15:0]).
e. Clear the KPKD status flag and synchronizer chain.
f. Set the KDIE control bit, and clear the KRIE control bit (avoid false release
events).
(now in standby mode, awaiting a keypress...)
2. Keypress interrupt detected
3. Begin keypad scanning routine
a. Disable keypad interrupts.
b. Write ones to KPDR[15:8], setting column data to ones.
c. Configure columns as totem-pole outputs.
d. Configure columns as open-drain.
e. Write a single column to zero, and write others to one.
f. Sample row inputs and save data. Multiple key presses can be detected on a
single column.
g. Repeat steps b to f for remaining columns.
h. Return all columns to zero in preparation for standby mode.
MMC2001
REFERENCE MANUAL
All manuals and user guides at all-guides.com
Freescale Semiconductor, Inc.
Column Pulled
Down
KEYPAD PORT
For More Information On This Product,
Go to: www.freescale.com
Column not
Pulled Down
Three Real
Key Presses
Ghost Key
Press
MOTOROLA
14-9
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