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Architecture
Debouncing time = (DEBOUNCETIME + 1) × 31 µs
Where the DEBOUNCETIME field value in the GPIO_DEBOUNCINGTIME register is from 0 to 255.
•
The debouncing feature must be enabled in the debouncing enable register (write 1 to the
corresponding DEBOUNCEENABLE bit in the GPIO_DEBOUNCENABLE register).
4.2.4.5
GPIO as a Keyboard Interface
The general-purpose interface can be used as a keyboard interface
channels based on the keyboard matrix = * c).
the input debounce feature enabled. The row channels are driven high with an external pull-up. Column
channels are configured as outputs and drive a low level.
When a keyboard matrix key is pressed, the corresponding row and column lines are shorted together
and a low level is driven on the corresponding row channel. This generates an interrupt based on the
proper configuration (see
When the keyboard interrupt is received, the processor can disable the keyboard interrupt and scan the
column channels for the key coordinates.
•
The scanning sequence has as many states as column channels: For each step in the sequence,
the processor drives one column channel low and the others high.
•
The processor reads the values of the row channels and thus detects which keys in the column are
pressed.
At the end of the scanning sequence, the processor establishes which keys are pressed. The keyboard
interface can then be reconfigured in the interrupt waiting state.
Figure 4-6. General-Purpose Interface Used as a Keyboard Interface
Device
L4
interconnect
generation
General Purpose Interface
536
General-Purpose I/O (GPIO) Interface
Preliminary
Section
4.2.3).
Row
channels
D
Interrupt
Column
channels
© 2011, Texas Instruments Incorporated
(Figure
Figure 4-6
shows row channels configured as inputs with
Keyboard matrix
I/O
pads
www.ti.com
4-6). You can dedicate
V
DD
....
....
SPRUGX9 – 15 April 2011
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