AT32F421 GPIO user guide
2020.07.30
12
Rev.1.0.0
PA13: SWDIO, AF pull-up
PA14: SWCLK, AF pull-down
Oscillator alternate function pin
When the oscillator is OFF (default state after reset), related pins can be used as GPIO
When the oscillator is enabled, the GPIO configuration of the related pins is invalid
When the oscillator is in bypass mode (use external clock source), OSC_IN/OSC32_IN acts as
an oscillator clock input pin, and OSC_OUT/OSC32_OUT can be used as GPIO.
Backup domain pin
When 1.2V domain is powered off (when the device enters standby mode), PC13/PC14/PC15
lost their GPIO functions. In this case, if GPIO is not configured by RTC as bypass, these pins
are set in analog input mode.
The following contents are not available in AT32F421 series:
Analog switch (power switch) can only allow a small amount of current (3mA), so in output
mode, there are some limits on using I/O functions of PC13/PC14/PC15: they can only work in
a moderate current sourcing/sinking strength mode, with a maximum of 30pF load, and these
I/Os must not be used as current source (such as driving LED)
