I've been having a play with my new 'scope (Rigol DS1102E) and have taken what can only be descibed as the lowest res screen shot since the Commodore PET .
This is the 8MHz PHI2 signal on my original 65C02 project. Given my lack of experience with electronics, I was wondering what people might make of the "square" wave signal itself, the edge rise and fall times, etc.

That actually looks reasonable. One thing to check, though: do you have your probes switched to x10 mode? You won't get the full bandwidth of the scope unless they are. Unless you're measuring very small signals, there's no reason to use x1.

You might think that a scope with 100MHz input bandwidth would give beautiful square traces from an 8MHz input. But it won't. Square waves contain lots of harmonics, with 1/n of the amplitude at n times the fundamental frequency. The scope will attenuate the higher harmonics, leaving the overshoot and ripple that you see.

Here's a quick simulation of what you get if you feed a perfect 8MHz square wave through a perfect 100MHz brick-wall filter. If I've got attaching pictures right...

In reality, the scope doesn't have a perfect filter, and your source is not a perfect square wave, so you won't get exactly that either. But it should show that even in a perfect world, you'll get an imperfect trace.

In addition to having the probes switched to x10 mode, another important thing is attaching the ground lead that's located on the end of the scope probe to ground of the device under test. Although it's possible to attach to some alternative ground point of the scope, the resulting trace may show artifacts such as increased ringing, and isn't appropriate for critical situations.

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Okey dokey. I've moved the scope ground lead to VSS on the 65C02 and checked the PHI2 pin. Previously I was using different points elsewhere with the scope ground close to the PSU ground pin.

Looks slightly different now:


Also, both the probes and the 'scope itself are in x10 mode, not x1 - been there, done that, got the T shirt previously .

Over-shoot on the rising and falling edges and the ringing look better and the rise/fall times themselves seem shorter - although that might just be happenstance.

This is what the output from bit 0 of one of the counters on my 6502 project looks like with my 200MHz scope...



Probes just crammed ad-hoc onto the breadboard through a 12 inch long wire.
So your signal looks about right!

Brad

Yep looks pretty much the same. Just got to figure out why my set up barely tolerates 10MHz. In theory, it should be good to 14 at least.

[edit] 12MHz FTW!

[edit #2] It was the stupid 12MHz oscillator can. Took out the straight non-badged 12MHz one and popped in a IQX0-350B 12.288MHz one and it all works.