User's Manual

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91 GPIO27 KEYCOL4 Keyboard row 4
Regular (dedicated) IO and alternate function IO have exactly the same characteristics
and can be programmed in the same way. The use of alternate function IO is subject
to some degree of limitation:
Signals which are assigned SD/MMC functionality are controlled by a single register
bit so that all nine signals are allocated to either memory card or GPIO; it not possible
individually allocate function.
Signals which are assigned keyboard functionality can be re-allocated GPIO
functionality on a pin-by-pin basis, providing anything from 1 to 9 additional GPIO.
Signals defined as keyboard functions are programmed to generate interrupts,
however the same pins programmed as GPIO do not have interrupt capability
associated with them.
GPIO is programmable for the following features
• either an input or output
• level-sensitive or transition-sensitive
• open drain or direct drive
• polarity (inversion)
• internal pull-up resistors
Signal labeled in the
Configurable IO table which are not being used for the indicated
alternative function be used as general purpose inputs or outputs; they are not
constrained to work in only one direction.
GPIO has a number of sharing (configuration) options. Sharing means that it is not
feasible to operate all the alternative features concurrently, however, with care,
dynamic switching from one feature to another is possible.
5.17.1 Embedded Applications
When a particular IO feature is required, the user sets the state of the relevant IO
blocks by disabling one set before enabling others.