Products > Test Equipment

USB Logic-Analyzer (sorry, long)

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0xdeadbeef:
While this has been discussed several times before I guess, I'd really appreciate some input on my thoughts regarding selecting an USB logic analyzer. E.g. if my assumptions are valid or if I overlooked something.

For the start, let's say I narrowed down the selection to the following two devices
Zeroplus LAP-C16128 (249€) + Trigger Module (~50€) (including VAT, but not shipping)
Intronix LogicScope (about 370€ including VAT and shipping)

I looked at at least a dozen of other USB LAs, but they all had severe limitations, crappy software or both. E.g. as far as I can tell the above two LAs are the only ones below 500€ that are able to trigger on pulse width. This excludes e.g. the devices from Saleae, USBee, Deditec, Hantek, RockyLogic and the Open Logic Sniffer. Well, I'm not so sure about the Logic Sniffer, but it appears to be a bit unstable and more like a thing to play around with than to work with. Please correct me if I'm wrong.

LogicScope
The trigger possibilities are pretty good: two levels and the possibility to trigger on the width of a level or pattern.
The memory per channel is very limited (2k Points), but the well designed compression (only changes are stored) still gives good memory depths (the better the less edges).
The most important protocols (like SPI, UART and CAN) are built in, but there is no way of adding additional protocols.

Zeroplus
Trigger possibilities are very simple. One level (channel edge, pattern) only. Triggering on width is only possible for one channel and only with the external Trigger Module which essentially creates an edge at another channel if the width/range condition for the connected channel is met. It's not clear to me if this makes it possible to combine the output of the trigger module with another channel as a pattern trigger. But it doesn't look like it.
There is an option for a protocol based trigger, but I assume this is not possible in real time (and costs another 46€).
The memory depth is ok (128k points per channel), unfortunately the compression algorithm is pretty basic, so even if the signal doesn't change at all, one sample is needed after 256 sample points.
The big advantage compared to all other USB LAs is the number of protocols. Apart from the fact that it already comes with all the most popular protocols, there's currently a special offer so you can select 30 additional protocols for free. As a result, the Zeroplus has nearly all the protocols I'll probably ever need. Which makes me a little enthusiastic to say the least.


While the LogicScope is the clear winner regarding trigger possibilities and the Zeroplus is the clear winner regarding the protocol analyzers, I'm a bit unsure who's the winner regarding the memory depth. It's clear that the LogicScope will always win for cases where there is very little activity and the ZeroPlus might take the lead if there is a lot of activity.

So I picked two use cases which I'm familiar with:

1) SENT (Single Edge Nibble Transmission)
A typical SENT message consists of a calibrations pulse and 8 nibble pulses (-> 18 edges) and lasts for 1ms.
While the SENT clock is usually 3µs, the SENT specification defines a time resolution of 100ns, so let's assume 10MSamples/s.

The Zeroplus has 128k Samplepoints: 131072/10000000 -> 13.1072ms
Assuming a 200:1 compression -> 2.62144s
-> 2.62144s/1ms -> 2621 messages

Intronix LogicScope can store 2k samples. I understand it only stores a sample if an edge occurs:
-> 2048/18 = 113.78 messages

2) SPI
A typical SPI communication with an output driver uses 1MBaud in our projects (due to EMC). A typical communication lasts about 60µs and needs about 128 CLK edges. Also the communication is usually started only every 10ms.
Let's assume a sampling rates of 10MSamples/s, which means an accuracy of 100ns to e.g. judge the timings between CS and CLK etc.

For the Zeroplus, we end up again with 13.1072ms (uncompressed) or 2.62144s (compressed)
-> 2.62144s/10ms -> 262 Messages

The LogicScope is limited again by the number of edges
-> 2048/128 = 16 Messages


This comparison is not completely fair, as obviously, the values for the LogicScope won't change for higher sampling speeds, resulting in better time resolution. Then again, even at 100MHz the ZeroPlus would win both comparisons. Even worse, if there are multiple devices on the SPI bus, the LogicScope would run out of memory much earlier as it had to sample the edges of the other devices as well.

This leaves me with the impression that in my typical use case scenarios, the Zeroplus provides better memory depth even at 100MHz, plus it clearly wins as protocol analyzer.
On the other hand the LogicScope has by far the better trigger options and will be superior for very short signals over a longer time, but this is simply not my typical use case.
Currently I tend to think that the Zeroplus would fit my needs better and essentially there is no other USB LA that offers so many protocols and allows to do a pulse width trigger at the same time.

So: any comments and are there other devices <500€ with width triggering that I overlooked?

[EDIT]
I overlooked the DigiView DV3100 which seems to combine the best of the two worlds (512K samples per channel with clever compression, 8 complex trigger levels with e.g. period triggers):
http://www.tech-tools.com/dv_dv3100.htm

As fas as I can tell, it would cost me around 455€ including shipping at VAT, which is a little more than I wanted to spend, but yeah well. Also there are not too many protocols implemented currently, but obviously the upcoming version of the SW will have the possibility to create own plugins via an API.

alm:
I believe the Open Logic Sniffer supports most of the triggering capability of a professional HP 16550A logic analyzer, so I would be surprised if it would be unable to trigger on pulse width. See the Dangerous Prototypes forum for more info.

'Dumb' USB bulk transfer based logic analyzers like the Saleae do all their triggering in software, so in theory there's no reason why the couldn't support pulse-width triggering, it's just a matter of implementing it in software. I'm not aware of any of them having released the software to do it, bugging them might help.

My impressions of the Zeroplus software were that it was horrible in the usability department, lots of tiny icons with no logical organization. Maybe they've improved their software since. They used to charge an arm and a leg for additional protocols (something like $80 for two). Do they allow you to build custom protocol analyzers?

The Intronix LogicPort (LogicScope?) is by far the closest to a professional tool, in my opinion. Most users don't have any issues with the memory limitations. Advanced triggers can make up for lack of memory to some degree.

0xdeadbeef:

--- Quote from: alm on September 25, 2011, 06:51:50 pm ---I believe the Open Logic Sniffer supports most of the triggering capability of a professional HP 16550A logic analyzer, so I would be surprised if it would be unable to trigger on pulse width. See the Dangerous Prototypes forum for more info.
--- End quote ---
My impression was that the Sniffer is very promising in theory, but in reality it's not really reliable at this point. Also the SW seems to be very weak to say the least.


--- Quote ---'Dumb' USB bulk transfer based logic analyzers like the Saleae do all their triggering in software, so in theory there's no reason why the couldn't support pulse-width triggering, it's just a matter of implementing it in software. I'm not aware of any of them having released the software to do it, bugging them might help.
--- End quote ---
Hm, that's a point. Then again, all triggering done in SW doesn't sound very reliable. And at least for now, none of the simple LAs supports advanced triggers. And hoping that this will change soon is as hoping that Intronix will provide more protocols or that the Open Sniffer will get a great GUI in the next weeks.


--- Quote ---My impressions of the Zeroplus software were that it was horrible in the usability department, lots of tiny icons with no logical organization. Maybe they've improved their software since. They used to charge an arm and a leg for additional protocols (something like $80 for two). Do they allow you to build custom protocol analyzers?
--- End quote ---
Well, neither the Intronix nor the Zeroplus SW is perfect, but I don't see such an advantage for the Intronix SW honestly. Both don't seem to support cutom plugins, but as pointed out before: with >30 (currently) free analyzers, the Zeroplus has more or less everything you'll ever need.


--- Quote ---The Intronix LogicPort (LogicScope?) is by far the closest to a professional tool, in my opinion. Most users don't have any issues with the memory limitations. Advanced triggers can make up for lack of memory to some degree.

--- End quote ---
Well, not always. Take the SENT example. There is really nothing you can trigger on in a SENT message apart from message length. Indeed what would be needed to trigger on a special message would be several sequential length triggers (e.g. 6 or 7). No USB LA (apart from maybe the DigiView) can do this. Futhermore, if an advanced serial message is embedded into SENT messages, it needs 18 messages to decode this serial message. This makes 324 edges for one serial message. It's quite obvious that the 2k buffer are quite limiting then.

0xdeadbeef:

--- Quote from: BoredAtWork on September 25, 2011, 07:21:38 pm ---However, all the USB logic analyzers have one fundamental problem, the fact that they are USB logic analyzers. They die the moment their Windows software dies. And this can happen with every hotfix, Windows update, service pack, new Windows version or even just the installation of some other software which happens to change an important windows setting, behavior or DLL.
--- End quote ---
I totally agree. That's e.g. why I ordered an Agilent arbitrary waveform generator in my company instead of an USB Lecroy Waveform generator. Even if the Agilent Windows SW id not usable in ten years, it will be still possible to upload waveforms from the USB stick.


--- Quote ---Therefore, don't consider a USB LA as a mid- or longterm investment if you have a job to do now. Get the one that does the job. If it happens to be good for other jobs, too, you are lucky. But if you want to treat the purchase as an investment then the reputation of the manufacturer is more important than features. A thousand features, but no working software means you have zero features.

--- End quote ---
I'm fully aware of this. Then again, regarding logic analyzers, there is not much of an alternative. The usual desktop LA is terribly loud and costs around 10k€ while the typical things you need to do can be done with a silent few hundred bucks USB LA. Anyway, also Intronix seems to be a very small company and regarding the state and last update of their website, I wouldn't be surprised if they wouldn't exist any more in two years or so. This is probably also true for any other of the <500€ LA companies. With this in mind, I'd had to get a LeCroy in the >1k€ range, but this is for my private stuff and I don't want to invest so much money right now.

seattle:
I have a logicport. The software is very good and rock solid. Rock solid as in, I leave it connected always, weeks on end, through hibernate and running, and at any time I can switch to that window and the logic analyzer is there waiting to do what I need.

The software copes readily with large data sets (meaning the compression works), and the protocol decoding works fine too.

However, as you note, if you are looking at something alongside a fast signal (like a clock), you will very quickly run up against the small memory. The 500 Msps speed is awesome too.

PS.  I agreed with BoredAtWork about USB a decade ago, but frankly for the last 5 years I've found USB on Windows to be (finally) plug and play and very reliable. Especially on Vista and later with silent driver installs. If a vendor does their job, it just works and continues to work. And I'm of the opposite opinion on desktop versus USB scopes. Desktop scopes feel like you are looking at the world through a pin hole. I'd rather spend an hour updating drivers every 4 years than have to stare at a scope screen with less pixels than my cellphone.

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