STM32 LED Blink example with explanation - Register level programming

Development board used : Nucleo - STM32F303RE 

1. Firmware - Led blink using register programming.

Using PORT A PIN 5 ( Nucleo built-in LED is connected to this pin)

Steps:

a) Enable the port PIN as output pin

To Enable a port pin as output, set corresponding GPIOx_MODER register 

Here in our case GPIOA_MODER is the register for PORT A 

For each port pin, there are 2 bits reserved in this register

So for pin 5, the bits are 10,11

To set pin 5 as output pin, set 10th bit as 1 (refer the below details for register bits)  

  

it can be done with below code 

GPIOA->MODER |= 1<<10;

 

b) Set pin HIGH or LOW

To change the state of GPIO pin, we need to update GPIOx_BSRR register.

 

To set PORTA 5th pin to HIGH , set 5th bit of  GPIOA_BSRR 

To make the port A 5th pin LOW , set 21st bit of GPIOA_BSRR (Refere above register details)

      GPIOA->BSRR |= 1<<5;        <--------- Make Port A 5th pin HIGH
       GPIOA->BSRR |= 1<<21;     <--------- Make PORT A 5th pin LOW.