Checking for TTL high signal with a scope?

[Chris Wilson]

How would I check for a TTL high signal on a test pin using my 7854 Tek scope? Or do I need something digital? If so, what is the minimum requirement? Thanks.

[SeanB]

DC coupled, 1V/div and see if the high level is over 3.5V. Low should be under 0.8V and the transition between should be fast, with no slow edges longer than around 2uS. A little ringing on the edges is normal or an artefact of the scope probe ground lead. W2AEW did a nice video on this recently, showing real TTL signals on his scope.

[Chris Wilson]

Thanks Sean, can't find Alan's video, and I like to think I watch them all, don't suppose you know what it was called do you? Would like to watch that, cheers.

[w2aew]

Thanks Sean, can't find Alan's video, and I like to think I watch them all, don't suppose you know what it was called do you? Would like to watch that, cheers.

Chris - here's the thread I posted it in...
https://www.eevblog.com/forum/beginners/new-video-oscilloscope-probe-ground-lead-length's-affect-on-signal-integrity/