First a disclaimer: I haven't used it. I've seen other scopes with similar functionality though.


Serial analysis plugins are showing up on scopes everywhere these days. I briefly surveyed the market last year, and also had a demonstration from a vendor. This sort of functionality has a lot of "wow" factor, and given access to a scope with such a feature, I'd use it regularly.

The thing is that scopes are generally intended for short term, timing mode analysis (e.g., sampling according to a scope-internal clock set at the start of the measurement) of AC waveforms. Having a serial bus decoder plugin doesn't change that much. Chances are, you'll still be wasting most of your sampling memory on artifacts that aren't terribly important for a strictly digital analysis of the serial data, and you'll be left without any really interesting triggering capabilities.

So, why use a scope for a serial bus? Because you're interested in measuring specific analog aspects of the bus signalling, like rise/fall time, clock duty cycle, steady state logic levels, checking for glitches, or something like that. For this kind of work, a scope cannot be replaced. Incidentally, a serial bus decoder plugin is by no means necessary for this sort of thing, but if it's there, it can certainly speed up the work a bit.



I agree with Jez' comment completely, assuming that by "serious bus work" he means "analysis of the digital data transferred over the bus", which is in sharp contrast to analyzing "analog aspects of the bus signalling", as I discussed earlier.

The bottom line is that a logic analyzer is not just a scope with 1-bit ADCs and a lot of channels. In reality, it's really quite a lot more than that. It is the foundation for an incredibly powerful protocol analysis system. Between the advanced triggering, the ability to sample based on clocking from the device under test, and very deep sample memories, it is possible to capture notable amounts of serial bus traffic and examine it for errors at the driver or application level.

As a more concrete example of what can be done with a logic analyzer, I recently captured 7 second snippets of audio from 6 PCM (e.g., I²S-like) channels, and an I²C control channel simultaneously. After a bit of post-processing, the result was a set of 6 time-syncrhonized .WAV audio files and a listing of I²C transactions, which were also timestamped and synchronized to the audio files. The insight these results provided into a suite of complex problems was absolutely invaluable, and capabilities like this are essential on just about any high-complexity embedded system project. Show me a scope that can do this, and you might convince me I don't need a logic analyzer. But in the meanwhile, I'll take both, regardless of whether the scope has a serial bus analysis feature.

--Sasha Jevtic