This page is the summary of me reading the reference manual, If there are missing info or incorrect info, please contact me at [email protected]

GPIO Main Features

• Set as output (we’ll use push-pull, basically just means it’ll drive a 1 and 0 constantly)
  • GPIOx_ODR will reflect the status of the output, we can read and write this easily to check the status of whichever pin
  • To set/reset, we can just use ODR, but it’s much faster to just go through BSRR. More info on that below
• Set as input to have floating, pull up/down or analog input. We can set this
  • Data is captured every clock cycle
• Set as Alternate Function (for example, GPIOA5 could be a UART pin (it’s NOT, just example))
• GPIO will use AHB clock, which is equal to SYSCLK (in the SYSCLK ticket we set the prescaler to 1)
• We have GPIO ports A→K

Alternate Function

• Each IO port has a multiplexer with 16 different AF inputs. We can configure this via GPIO_AFRL (pin 0-7) and GPIO_AFRH (pin 8-15)
• Set the Pins to AF mode via GPIO_MODER
• Then configure the pin as normal
• For more information, there’s a whole process on how to set pins to AF’s on the datasheet

Input / Output

Below are the registers used to configure GPIO

• GPIOx_MODER - Select the mode we want to use
• GPIOx_OTYPER - output type if we choose output
• GPIOx_OSPEEDR - choose output speed
• GPIOx_PUPDR - choose pull up or pull down for “default” starting state
  • Pin will be left floating if not used
  • PD - 10, pin will be LOW when idle
  • PU - 01, pin will be HIGH when idle
  • This is pretty important for input pins as they can definitely be idle
  • For output, since we’re doing push-pull, it will never be idle