Alternate Functions (GPIO)
- The output buffer can be enabled (open drain or push-pull).
- The output buffer is controlled by connected peripheral.
- 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.
Programming Instructions
Depending on the alternate function you have to configure the pins as:
Configuration Registers
GPIOx_MODER - Mode register
| Pin x | 10 | Alternate function mode |
GPIOx_AFRL/H - Alternate function register (low / high)
| Pin x | 0000 | AF0: RTC, MCO, Tamper, SWJ, Trace |
| 0001 | AF1: Timer 1, Timer 2 | |
| 0010 | AF2: Timer 3..5 | |
| 0011 | AF3: Timer 8..11 | |
| 0100 | AF4: I²C 1..3 | |
| 0101 | AF5: SPI 1..6 | |
| 0110 | AF6: SPI 2/3, SAI 1 | |
| 0111 | AF7: SPI 3, USART 1..3 | |
| 1000 | AF8: USART 6, UART 4/5/7/8 | |
| 1001 | AF9: CAN 1/2, Timer 12..14, LCD | |
| 1010 | AF10: USB OTG HS/FS | |
| 1011 | AF11: Ethernet | |
| 1100 | AF12: FMC, SDIO, USB OTG FS | |
| 1101 | AF13: DCMI | |
| 1110 | AF14: LCD | |
| 1111 | AF15: Event Out |
GPIOx_PUPDR - GPIO 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 |