STM32F4: GPIOx_AFRL/H value vs. GPIOx_MODER AF mode

picguy2 · ‎2014-07-24

Posted on July 25, 2014 at 02:53

What is the use of the GPIOx_MODER Alternate function mode? Is it needed when an appropriate non-zero value is put into GPIOx_AFRL/H? Is the GPIOx_MODER alternate function mode value only needed for those few alternates using GPIOx_AFRL/H AF=0?

Does the alternate function take over the entire GPIO port bit. Or are GPIOx_OSPEEDR and GPIOx_PUPDR settings used as specified by the values stored in these registers?

(I have never had the occasion to use any AF=0 alternate functions. When setting a non-zero alternate function have a tendency to set alternate function mode in GPIOx_MODER. My guess is that I am doing something unnecessary.)

#gpio-alternate-function

waclawek.jan · ‎2014-07-25

Posted on July 25, 2014 at 12:01

You set _MODER to AF for any of the alternate function, both zero and nonzero _AFRL/H.

> Does the alternate function take over the entire GPIO port bit.

No. The mapped peripheral determines the direction (IN/OUT), but you still have speed, pullup/down and open-collector/push-pull under ''manual'' control through the respective registers.

JW