STM32W108HB datasheet(50/179 Pages) STMICROELECTRONICS

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General-purpose input/outputs

STM32W108CB, STM32W108HB

50/179

Doc ID 16252 Rev 2

Input mode

Input mode is used both for general purpose input and for on-chip peripheral inputs. Input

floating mode disables the internal pull-up and pull-down resistors, leaving the pin in a high-

impedance state. Input pull-up or pull-down mode enables either an internal pull-up or pull-

down resistor based on the GPIO_PxOUT register. Setting a bit to 0 in GPIO_PxOUT

enables the pull-down and setting a bit to 1 enables the pull up.

When configured in input mode:

●

The output drivers are disabled.

●

An internal pull-up or pull-down resistor may be activated depending on

GPIO_PxCFGH/L and GPIO_PxOUT.

●

The Schmitt trigger input is connected to the pin.

●

Reading GPIO_PxIN returns the input at the pin.

●

The input is also available to on-chip peripherals.

Output mode

Output mode provides a general purpose output under direct software control. Regardless

of whether an output is configured as push-pull or open-drain, the GPIO's bit in the

GPIO_PxOUT register controls the output. The GPIO_PxSET and GPIO_PxCLR registers

can atomically set and clear bits within GPIO_PxOUT register. These set and clear registers

simplify software using the output port because they eliminate the need to disable interrupts

to perform an atomic read-modify-write operation of GPIO_PxOUT.

When configured in output mode:

●

The output drivers are enabled and are controlled by the value written to

GPIO_PxOUT:

●

In open-drain mode: 0 activates the N-MOS current sink; 1 tri-states the pin.

●

In push-pull mode: 0 activates the N-MOS current sink; 1 activates the P-MOS current

source.

●

The internal pull-up and pull-down resistors are disabled.

●

The Schmitt trigger input is connected to the pin.

●

Reading GPIO_PxIN returns the input at the pin.

●

Reading GPIO_PxOUT returns the last value written to the register.

Note:

Depending on configuration and usage, GPIO_PxOUT and GPIO_PxIN may not have the

same value.

Alternate output mode

In this mode, the output is controlled by an on-chip peripheral instead of GPIO_PxOUT and

may be configured as either push-pull or open-drain. Most peripherals require a particular

output type - TWI requires an open-drain driver, for example - but since using a peripheral

does not by itself configure a pin, the GPIO_PxCFGH/L registers must be configured

properly for a peripheral's particular needs. As described in Section 6.1.2: Configuration on

page 47, when more than one peripheral can be the source of output data, registers in

addition to GPIO_PxCFGH/L determine which to use.

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