what is speed of GPIO?

[twoaten]

Posted on March 27, 2014 at 02:25

I'm really wondering what speed selection of GPIO is.

There are some options to select GPIO Speed, such as 2MHz, 25MHz, 50MHz and 100MHz.What does the speed mean?Which value is selected generally?

[Tesla DeLorean]

Posted on March 27, 2014 at 02:33

It refers to slew-rate control, the ability to drive a rapid edge into a capacitive load. You should pick a speed which is appropriate to the signals the peripheral is generating. Unnecessarily high speed will consume more power, result in over/under shoot, and more EMI

[twoaten]

Posted on March 27, 2014 at 02:43

Thanks a lot.

I'm using STM32F407. In general use of GPIO, such as LED Control, is it enough to select 2MHz(low speed)? 

[Tesla DeLorean]

Posted on March 27, 2014 at 02:47

Indeed, as would a USART at 115200 baud.

A pin for SDIO, perhaps 25-50 MHz, and FSMC 50-100 MHz

[twoaten]

Posted on March 27, 2014 at 03:22

It some confused me.

even if GPIO port is configured to Peripheral, such as UART, then,selection of GPIO speed is depends on UART baudrate?I thought the GPIO speed doesn't matter when that GPIO is configured to peripheral.