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RM0365
General-purpose I/Os (GPIO)
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The LOCK sequence (refer to
Section 10.4.8: GPIO port configuration lock register
) can only be performed using a word (32-bit long) access to the
GPIOx_LCKR register due to the fact that GPIOx_LCKR bit 16 has to be set at the same
time as the [15:0] bits.
For more details refer to LCKR register description in
configuration lock register (GPIOx_LCKR) (x = A..H)
.
10.3.7
I/O alternate function input/output
Two registers are provided to select one of the alternate function inputs/outputs available for
each I/O. With these registers, the user can connect an alternate function to some other pin
as required by the application.
This means that a number of possible peripheral functions are multiplexed on each GPIO
using the GPIOx_AFRL and GPIOx_AFRH alternate function registers. The application can
thus select any one of the possible functions for each I/O. The AF selection signal being
common to the alternate function input and alternate function output, a single channel is
selected for the alternate function input/output of a given I/O.
To know which functions are multiplexed on each GPIO pin, refer to the device datasheet.
10.3.8
External interrupt/wakeup lines
All ports have external interrupt capability. To use external interrupt lines, the port must be
configured in input mode.
Section 13.2: Extended interrupts and events controller (EXTI)
and
to
Section 13.2.3: Wakeup event management
.
10.3.9 Input
configuration
When the I/O port is programmed as input:
•
The output buffer is disabled
•
The Schmitt trigger input is activated
•
The pull-up and pull-down resistors are activated depending on the value in the
GPIOx_PUPDR register
•
The data present on the I/O pin are sampled into the input data register every AHB
clock cycle
•
A read access to the input data register provides the I/O state
shows the input configuration of the I/O port bit.