Help umderstanding this rising/falling edge

[AlfBaz]

Messing around with the PWM module on a PIC18F4550, I decided to up the frequency to just under 50kHz and all of a sudden I noticed the pulses aren't looking very square anymore.

Looking a little closer I realised the lower frequency waves looked squarer because the scopes time base was increased to fit a couple of cycles. Expanding the edge at these frequencies yielded the same edge.

Thinking it may be the PWM module I simply toggled an output... same thing

The 18f4550 supply is rated from 4.2 to 5.5V, yet it seems the output drives to 3.3V then just "coasts" to VDD

The images bellow are of the edge at 50us and 1us time base
In the 1us image the sharp rise has 2 slopes if you expand even more. The first slope takes 6ns to get to about 2.16V the second is an additional 20ns to reach 3.3V. The total time for the initial edge is 26ns to 3.3V shown in the image. Its then another 7.8us to reach VDD

Is this normal?

[AlfBaz]

Oh I forgot to mention, the outputs look similar regardless of wether they are loaded or open cct

[MikeK]

Have you adjusted probe compensation?

[AlfBaz]

Have you adjusted probe compensation?

Yes

[AlfBaz]

Hey Mike just tried another probe, problem solved... Thank you very much 

[marshallh]

Watch w2aew's video about ground leads.
Also, the rounded leading edge like that smacks of capacitive loading. I had a similar phenomenon with a pcb failure causing that kind of issue.
You can also see these kinds of waveforms on weak outputs driving long cables (also capacitive loads)