Analog Configuration; Using The Hse Or Lse Oscillator Pins As Gpios; Using The Gpio Pins In The Rtc Supply Domain; Figure 22. High Impedance-Analog Configuration - STMicroelectronics RM0365 Reference Manual

General-purpose I/Os (GPIO)
10.3.12

Analog configuration

When the I/O port is programmed as analog configuration:
•
The output buffer is disabled
•
The Schmitt trigger input is deactivated, providing zero consumption for every analog
value of the I/O pin. The output of the Schmitt trigger is forced to a constant value (0).
•
The weak pull-up and pull-down resistors are disabled by hardware
•
Read access to the input data register gets the value "0"
Figure 22
10.3.13

Using the HSE or LSE oscillator pins as GPIOs

When the HSE or LSE oscillator is switched OFF (default state after reset), the related
oscillator pins can be used as normal GPIOs.
When the HSE or LSE oscillator is switched ON (by setting the HSEON or LSEON bit in the
RCC_CSR register) the oscillator takes control of its associated pins and the GPIO
configuration of these pins has no effect.
When the oscillator is configured in a user external clock mode, only the pin is reserved for
clock input and the OSC_OUT or OSC32_OUT pin can still be used as normal GPIO.
10.3.14

Using the GPIO pins in the RTC supply domain

The PC13/PC14/PC15 GPIO functionality is lost when the core supply domain is powered
off (when the device enters Standby mode). In this case, if their GPIO configuration is not
bypassed by the RTC configuration, these pins are set in an analog input mode.
For details about I/O control by the RTC, refer to
on page
163/1080
shows the high-impedance, analog-input configuration of the I/O port bit.

Figure 22. High impedance-analog configuration

724.
DocID025202 Rev 7
Section 27.3: RTC functional description
RM0365