I have tried changing the GPIO output speed and then toggled the output and monitored it on a scope. There is a slight increase in rise time with the speed set to 50MHz, but otherwise very little difference. Why is this?

[waclawek.jan]

Which mcu?

Try to load the output with significant capacitance, tens of pF. Also, switch on the compensation cell, if your mcu has one.

JW

[Bob S]

What kind of load to you have on that pin? Is it connected to anything? Depending on the load you may not see any (or much) difference. For example, a pin with no connection or one driving a high-impedence/low capacitance load won't show much difference. A pin driving a low impedence and/or high capacitance load will show a big difference.