STM8S datasheet(110/467 Pages) STMICROELECTRONICS

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General purpose I/O ports (GPIO)

RM0016

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DocID14587 Rev 14

11.7.4

Schmitt trigger

On all I/Os with an analog input, it is possible to disable the Schmitt trigger, even if the

corresponding ADC channel is not enabled. The two registers ADC_TDRH and ADC_TDRL

allow to disable the Schmitt trigger.

Setting one bit in these registers leads to disabling the corresponding Schmitt trigger input

buffer.

In case an I/O is used as analog input, and the corresponding ADC channel is enabled

(CH[3:0] bits in ADC_CSR register), the Schmitt trigger is disabled, whatever the status of

the corresponding bit in ADC_TDRH or ADC_TDRL registers.

11.7.5

Analog function

Selected I/Os can be used to deliver analog signal to ADC, Comparators or DAC periphery.

The GPIO pin have to be configured in the input floating configuration without interrupt

(default state) to use it for analog function. The current consumption of the IO with enabled

analog function can be reduced by disabling unused Schmitt trigger in IO input section

either by ADC_TRIGRx register in ADC interface (see Section 14.3.15: Schmitt trigger

disabling) or by switching on a corresponding analog switch in RI by setting corresponding

CHxE bit in RI_IOSRx (see Section 11.2.2: I/O groups). See the product datasheet for pins

with analog functions.

11.8

Output mode details

11.8.1

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 output pins must be set-up as push-pull, fast slope for optimal operation.

11.8.2

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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