SPI vs GPIO - Alternate Functions (AF)

[LucasStartTech]

@Tesla DeLorean Hi! Thank you for helping me with the BOOTING process. However, I have a question about the peripherals. I am planning to control a TFT screen that requires 40 pins and RGB protocol. At first, I was planning to choose random GPIOs to build the protocol (I am trying to learn by making it rather than just applying something already built), and I noticed that if I choose to use LTDC, some pins light up, as well as for connectivity like SPI... The pins selected by the IDE to do such tasks have any special characteristics? do they toggle faster? or could I do just the same applying the protocol to any other random set of GPIOs?

[Andrew Neil]

Just to add to the confusion, STM32 also has "additional functions" - typically for the analogue features.

Typically, these are selected just by enabling the "additional" function.

[Tesla DeLorean]

With the F469 the pins committed to the LCD RGB signals and SDRAM FMC have very few options/alternatives. The pin-mux routing internal peripherals to pins is relatively fixed and inflexible, ie it's not a giant cross-bar switch permitting an anything-to-anything wiring.

The "Table 12. Alternate function" might be most illustrative of the options

https://www.st.com/resource/en/datasheet/stm32f469ii.pdf#page=73