I/O Alternate Function Input/Output; External Interrupt/Wakeup Lines; Input Configuration - STMicroelectronics STM32F05 series Reference Manual

RM0091
The LOCK sequence (refer to
(GPIOx_LCKR) (x =
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 please refer to LCKR register description in
configuration lock register (GPIOx_LCKR) (x =
8.3.7

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, you can connect an alternate function to some other pin as
required by your 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 one I/O.
To know which functions are multiplexed on each GPIO pin, refer to the device datasheet.
8.3.8

External interrupt/wakeup lines

All ports have external interrupt capability. To use external interrupt lines, the port must be
configured in input mode, refer to the Extended interrupts and events controller (EXTI) and
to the Wakeup event management section.
8.3.9

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
Figure 14
Section 8.4.8: GPIO port configuration lock register
A..B)) can only be performed using a word (32-bit long) access to the
shows the input configuration of the I/O port bit.
Doc ID 018940 Rev 1
General-purpose I/Os (GPIO)
Section 8.4.8: GPIO port
A..B).
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