RM0312 datasheet(79/275 Pages) STMICROELECTRONICS

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RM0312

General purpose I/O ports (GPIO)

10.7

Input mode details

10.7.1

Alternate function input

Some I/Os can be used as alternate function input. For example as the port may be used as

the input capture input to a timer. Alternate function inputs are not selected automatically,

you select them by writing to a control bit in the registers of the corresponding peripheral.

For Alternate Function input, you should select floating or pull-up input configuration in the

DDR and CR1 registers.

10.7.2

Interrupt capability

Each I/O can be configured as an input with interrupt capability by setting the CR2x bit while

the I/O is in input mode. In this configuration, a signal edge or level input on the I/O

generates an interrupt request.

Falling or rising edge sensitivity is programmed independently for each interrupt vector in

the EXTI_CR[2:1] registers.

External interrupt capability is only available if the port is configured in input mode.

Interrupt masking

Interrupts can be enabled/disabled individually by programming the corresponding bit in the

configuration register (Px_CR2). At reset state, the interrupts are disabled.

If a pin alternate function is TLI, use the Px_CR2 bit to enable/disable the TLI interrupt. The

TLI interrupt is associated to a dedicated interrupt vector.

10.8

Output mode details

10.8.1

Alternate function output

Alternate function outputs provide a direct path from a peripheral to an output or to an I/O

pad, taking precedence over the port bit in the data output latch register (Px_ODR) and

forcing the Px_DDR corresponding bit to 1.

An alternate function output can be push-pull or pseudo-open drain depending on the

peripheral and Control register 1 (Px_CR1) and slope can be controlled depending on the

Control register 2 (Px_CR2) values.

Examples:

SPI outputs must be set-up as push-pull. The slope of SPI outputs is controlled by hardware

and configured in fast mode to enable an optimal operation. The user must then keep the

CR2 slope control bit cleared to avoid spurious interrupts.

10.8.2

Slope control

The maximum frequency that can be applied to an I/O can be controlled by software using

the CR2 bit. Low frequency operation with improved EMC behavior is selected at reset.

Higher frequency (up to 10 MHz) can be selected if needed. This feature can be applied in

either open drain or push-pull output mode on I/O ports of output type O3 or O4. Refer to the

pin description tables in the datasheets for the specific output type information for each pin.

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