Device
General-purpose interface
Column
channels
Row
channels
Interrupt
generation
D
V
DD
Keyboard matrix
....
....
I/O
pads
L4
interconnect
gpif-003
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General-Purpose Interface Environment
Figure 25-3. General-Purpose Interface Used as a Keyboard Interface
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
, Interrupt and Wakeup).
When the keyboard interrupt is received, the processor (the MPU and/or IVA2.2 subsystem) 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.
3467
SWPU177N – December 2009 – Revised November 2010
General-Purpose Interface
Copyright © 2009–2010, Texas Instruments Incorporated
