STM32F411CEU6 Black Pill

Fig. 1. STM32F411CEU6 Black Pill, 2x20 2.54 mm, 53 x 21 mm. Hover or tap a signal to light up every pin that carries it.

• Every pin is 5 V tolerant on the F401. On the F411 two are not: PA0 and PB5 are 3.3 V only.
• The USB-C works out of the box, with the right D+ pull-up fitted. That alone is the reason to pick this over a Blue Pill.
• PC13 drives the blue LED and sinks it, so low turns it on. PC13, PC14 and PC15 are limited to 3 mA.
• There is a user button labeled KEY on PA0, active low, and it is already debounced in hardware. Holding BOOT0 at reset enters the built-in DFU bootloader over USB, so you can flash with dfu-util and no programmer at all.
• PA13 and PA14 are SWDIO and SWCLK on the 4-pin header at the bottom edge, not on the side headers.
• PA4, PA5, PA7 and PB4 also go to the optional on-board SPI flash footprint. If your board has the chip fitted, those four are shared.
• PB2 is BOOT1 and PC14 and PC15 carry the 32.768 kHz crystal, so treat all three as spoken for.
• The 5V header pins tie straight to USB VBUS with no protection. Do not back-feed them while USB is plugged in.

• Blink the on-board LED on PC13

  CMSIS, no HAL

  #include "stm32f4xx.h"
  
  /* F4 is a different GPIO block from the F1. Clock gating moved to
     AHB1, and the four-bit CRL/CRH scheme is gone. */
  RCC->AHB1ENR |= RCC_AHB1ENR_GPIOCEN;
  
  /* MODER is 2 bits per pin: 01 = general purpose output. */
  GPIOC->MODER &= ~(3u << (13 * 2));
  GPIOC->MODER |=  (1u << (13 * 2));
  
  GPIOC->OTYPER  &= ~(1u << 13);        /* push-pull */
  GPIOC->OSPEEDR &= ~(3u << (13 * 2));  /* low speed is fine for an LED */
  
  GPIOC->BSRR = GPIO_BSRR_BR13;         /* LED on, active low */
  GPIOC->BSRR = GPIO_BSRR_BS13;         /* LED off */

  Code written for an F1 Blue Pill will not compile here. CRL and CRH do not exist on the F4, the clock enable moved from APB2ENR to AHB1ENR, and MODER is two bits per pin instead of four.

Table 1. Pin assignments.