Logic analyzer: Was Better (perhaps) A500 compatibility

[gralco]

Originally Posted by zero

Yeah, it would be fine if they had compression but they don't seem to. Useless for the stuff I am working on like USB (12MHz). I find that even 2x the signal frequency is unreliable, e.g. I have a 24MHz USB LA but it can rarely decode USB packets and most USB peripherals use a 48MHz sample clock.

In the case of the SDS2000X Plus you could still measure those faster clocks with its LA but you'd have to narrow the horizontal window.

[Daedalus]

Originally Posted by zero

I find that even 2x the signal frequency is unreliable, e.g. I have a 24MHz USB LA but it can rarely decode USB packets and most USB peripherals use a 48MHz sample clock.

Your sampling rate has to be much higher than whatever you're trying to measure, especially if your LA isn't synchronised with the source clock. A 24MHz sampling rate simply isn't enough to accurately capture a 12MHz signal. An absolute bare minimum would be about 1:4 just to be able to capture each transition, so you really need a minimum of 50MHz sample rate to deal with a 12MHz signal. DSLogic recommend a 1:10 ratio, so 120MHz sampling rate for a 12MHz signal.

[zero]

Originally Posted by Daedalus

Your sampling rate has to be much higher than whatever you're trying to measure, especially if your LA isn't synchronised with the source clock. A 24MHz sampling rate simply isn't enough to accurately capture a 12MHz signal. An absolute bare minimum would be about 1:4 just to be able to capture each transition, so you really need a minimum of 50MHz sample rate to deal with a 12MHz signal. DSLogic recommend a 1:10 ratio, so 120MHz sampling rate for a 12MHz signal.

Yes, that's what I'm saying. Fortunately the USB protocol decoder in Sigrok is very forgiving and will cope just fine at 50MHz, and can even decode a lot of it at 24MHz.

Another reason why I like USB LAs, the protocol decoding tends to be better and you can always hack it or write your own.