STM32F4 Discovery MCO1 from HSI clock source looks like an analog signal when I expected it to be digital.

[Xeyler]

I used CubeMX to point HSI(16 MHz) to Master Clock Output 1(no prescaler). I hooked it up to my o-scope and saw the signal in the following picture. It's obviously not a digital signal, but shouldn't it be? What's going on here?

[Tesla DeLorean]

Will take me a few to fire one up, perhaps you can pull a 10X scope probe and try that..

[Xeyler]

I hooked up a 10x probe and it looks a lot closer to square. I'm guessing the 1x probe interfered with the signal? I didn't realized it could have such a drastic effect... What qualities of signals should I look out for when deciding which probe to use?

[Tesla DeLorean]

At high frequencies go for 10x mode

EEVBlog Dave Jones had a great video on this, seem to recall something around 6 MHz.

[Tesla DeLorean]

This was with GPIO_InitStructure.Speed = GPIO_SPEED_HIGH; given the ringing and the load I think I can use a less aggressive slew rate.