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General-purpose input/outputs<br />
<strong>STM32W108C8</strong><br />
8.1.6 GPIO modes<br />
Analog mode<br />
Note:<br />
Analog mode enables analog functions, and disconnects a pin from the digital input and<br />
output logic. Only the following GPIO pins have analog functions:<br />
● PA4, PA5, PB5, PB6, PB7, and PC1 can be analog inputs to the ADC.<br />
● PB0 can be an external analog voltage reference input to the ADC, or it can output the<br />
internal analog voltage reference from the ADC.<br />
● PC6 and PC7 can connect to an optional 32.768 kHz crystal.<br />
When an external timing source is required, a 32.768 kHz crystal is commonly connected to<br />
PC6 and PC7. Alternatively, when PC7 is configured as a digital input, PC7 can accept a<br />
digital external clock input.<br />
When configured in analog mode:<br />
● The output drivers are disabled.<br />
● The internal pull-up and pull-down resistors are disabled.<br />
● The Schmitt trigger input is connected to a high logic level.<br />
● Reading GPIO_PxIN returns a constant 1.<br />
Input mode<br />
Input mode is used both for general purpose input and for on-chip peripheral inputs. Input<br />
floating mode disables the internal pull-up and pull-down resistors, leaving the pin in a highimpedance<br />
state. Input pull-up or pull-down mode enables either an internal pull-up or pulldown<br />
resistor based on the GPIO_PxOUT register. Setting a bit to 0 in GPIO_PxOUT<br />
enables the pull-down and setting a bit to 1 enables the pull up.<br />
When configured in input mode:<br />
● The output drivers are disabled.<br />
● An internal pull-up or pull-down resistor may be activated depending on<br />
GPIO_PxCFGH/L and GPIO_PxOUT.<br />
● The Schmitt trigger input is connected to the pin.<br />
● Reading GPIO_PxIN returns the input at the pin.<br />
● The input is also available to on-chip peripherals.<br />
Output mode<br />
Output mode provides a general purpose output under direct software control. Regardless<br />
of whether an output is configured as push-pull or open-drain, the GPIO's bit in the<br />
GPIO_PxOUT register controls the output. The GPIO_PxSET and GPIO_PxCLR registers<br />
can atomically set and clear bits within GPIO_PxOUT register. These set and clear registers<br />
simplify software using the output port because they eliminate the need to disable interrupts<br />
to perform an atomic read-modify-write operation of GPIO_PxOUT.<br />
59/215 Doc ID 018587 Rev 2
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