How can i switch on LED on STM32F1 GPIO pin PA2?

问题

How can i switch on the LED on PA2 GPIO (STM32F103C8T6), using standard registry configuration.

RCC-> APB2ENR |= (1<<2);
GPIOA->CRL |= (1<<9);
GPIOA->ODR |= (1<<3);

Does not work for me. Could you please advice where i make mistake?

回答1:

As per the reference manual, the GPIOA CRL registers resets as 0x4444 4444 (See section 9.2.1 of the reference manual). When you execute the following command:

GPIOA->CRL |= (1<<9);

you are setting the MODE bits of PA2 to 10 (Output mode, max speed 2 MHz). But due to the inital register initialization, the CNF2 bits are 01, which is open-drain configuration. You should initialize PA2 with the following instead

GPIOA->CRL &= ~(0b0000<<8);
GPIOA->CRL |= (0b0010<<8);

This ensures that both MODE2 and CNF2 are both set so the pin acts as an output with a push-pull configuration

来源：https://stackoverflow.com/questions/59920888/how-can-i-switch-on-led-on-stm32f1-gpio-pin-pa2