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can I connect ADC pins right to my digital output pins?

Question asked by belomutskiy.andrey on Nov 12, 2012
I am using same stm32 board to both generate some signals (plain PAL_MODE_OUTPUT_PUSHPULL pins) and validate my code by drawing build-in ADC readings. Everything was OK - what I saw on the screen was what I was expecting to see, till I needed more channels and maybe higher frequencies (like 50Khz ADC via PWM and ).

Bottom line - the issue could totally be on the software side, but I want to double-check since I am not really good with the analog side of this: is it OK to simply connect output pins with ADC input pins without placing anything in between? Problem is some pairs of inputs and outputs work fine but simply changing the wiring between pairs messes up the reading.

Probably easiest to show an example: this picture is fine - two 50% waves, as expected:

And here is the same stuff but with outputs connected with same ADC channels in the other order:

you can see the lower channel is not 50% cycle as it should be.

Software issue? Hardware issue?