General Purpose Output
- The output buffer is enabled (open drain or push-pull).
- The Schmitt trigger input is active.
- The pull-up and -down resistors are active, according to PUPDR.
- Input data is sampled every AHB clock.
- Input data register holds I/O state.
- Output data register holds last written value.
Programming Instructions
Enable Peripheral
Make sure the peripheral is enabled:
- Enable GPIOx in
RCC→AHBENR[0].
Setup output mode
Configure the MODE and PUPDR as well as the output type and speed register,
for every pin that should act as digital output:
- Write
0x01to the corresponding fields inGPIOx→MODE. - Configure pull-up / -down in
GPIOx→PUPDR. - Configure output type in
GPIOx→OTYPER.
(in conjunction withGPIOx→PUPDR) - Configure output speed in
GPIOx→OSPEEDR.
Configuration Registers
GPIOx_MODER - Port mode register
| Pin x | 01 | Output mode |
GPIOx_PUPDR - Port pull-up / pull-down register
| Pin x | 00 | No pull-up, pull-down (reset state) |
| 01 | Pull-up | |
| 10 | Pull-down | |
| 11 | Reserved |
GPIOx_OTYPER - Port output type register
| Pin x | 0 | Output type: push-pull (reset state) |
| 1 | Output type: open-drain |
GPIOx_OSPEEDR - Port output speed register
| Pin x | 00 | Speed: 2 MHz (reset state) |
| 01 | Speed: 10 MHz | |
| 10 | Speed: 50 MHz | |
| 11 | Speed: 100 MHz |
Data Registers
GPIOx_ODR - Port output data register
| ODx | 0 | Clear/reset pin x |
| 1 | Set pin x |
GPIOx_BSRR Port bit set / reset register
| BSx | 0 | No effect |
| 1 | Set pin x | |
| BRx | 0 | No effext |
| 1 | Clear/reset pin x |