STM8S datasheet(109/467 Pages) STMICROELECTRONICS

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RM0016

General purpose I/O ports (GPIO)

113

11.7

Input mode details

11.7.1

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.

11.7.2

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.

11.7.3

Analog channels

Analog I/O channels can be selected by the ADC peripheral. The corresponding input and

output stages are then automatically disabled. As mentioned in the next section, the input

Schmitt trigger should be disabled in the ADC_TDR register when using the analog

channels.

Table 23. Recommended and non-recommended configurations for analog input

DDR

CR1

CR2

ADC_TDR

Configuration

Comments

Floating Input without interrupt,

Schmitt trigger disabled

Recommended analog input

configuration

Input with pull-up enabled

Not recommended for analog input when

analog voltage is present since these

configurations cause excess current flow

on the input pin.

Both input and output stages are

disabled on ADC selected channel.

Output

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