MSO and USB LA owners - Page 1
Forum section: electronics / testgear

author: Howardlong
author_rank: Super Contributor
timestamp: February 15, 2016, 08:37:22 am
content: So there's a school of thought that says an MSO nowadays is of limited value compared to a DSO plus a USB LA like a Saleae or Logicport for example.Typically MSOs have higher sample rates than USB LAs, have time correlation with analogue channles and offer much more comprehensive triggering options, whereas USB LAs offer a much larger screen and sometimes much deeper memory.So which do you prefer?

author: Sal Ammoniac
author_rank: Super Contributor
timestamp: July 28, 2016, 02:31:37 am
content: I prefer an MSO for the reasons you state.I have a Saleae Pro 8 that I use for debugging slow serial protocols, such as I2C, but it's really not much more than a toy. You can't set up anything other than a very simple trigger, and you can't group channels together in a bus like you can with a real analyzer. This last one makes it almost useless to me for any kind of hard-core debugging.The Saleae is big on eye candy but lacking in functionality.

author: LabSpokane
author_rank: Super Contributor
timestamp: July 28, 2016, 04:50:11 am
content: MSOs are obviously much better at analyzing signal integrity and timing issues. USB Logic analyzers are much better at collecting long streams of decoded data for subsequent analysis.Both have a place. Both have limitations that make one better than the other.

author: Berni
author_rank: Super Contributor
timestamp: July 28, 2016, 06:18:26 am
content: I have two MSO scopes yet they rarely get any use. Thing is that almost everything is serial these days so usually the 4 analog channel are enough. It's always better to use those if you have them because it shows you any signal integrity issues, floating, two outputs fighting on a line etc.When my saleae USB LA comes in then it is for looking trough large amounts of data where I can just record for seconds or even minutes and then ponder over it at my own pace. It's easier to look through it in a PC and I can export it in to other tools.If I worked on old computers with parallel data buses going around that's where a real logic analyser comes in handy.

author: D3f1ant
author_rank: Frequent Contributor
timestamp: July 28, 2016, 08:06:26 am
content: Long captures of data I use a usb LA, when debugging a mixed analog digital, the mso is more useful. Seeing if there is psu glitches in time with bus errors a mso is ideal. But even the longest deep memory scope can't compare to streaming data in via usb for offline analysis, we're talking gigabyte captures. Tiny scope screens are not ideal for viewing 8+ channels...a pc just handles it better. I would buy a mso scope first, its more versatile and gets used more often. Basic LA like saleae is cheap enough that can pick one up if/when you need it.

author: Performa01
author_rank: Super Contributor
timestamp: July 28, 2016, 10:40:26 am
content: It obviously depends on the specific task and on the quality of both the MSO and LA.Typically, an LA is more powerful than the digital part of an MSO, because it can have more channels and more sophisticated trigger options by providing several trigger levels to set up a trigger sequence. The biggest advantage is the huge choice of protocols available for bus decoding.The MSO on the other hand, has the correlation between analog and digital channels and provides advanced trigger modes like pulse width, pulse timeout, runt and maybe some others, that are normally not available for digital channels, neither on the MSO nor on the LA. There are usually only few Protocols available for bus decoding.A good USB-LA isn’t cheap and can easily exceed the price of a low cost MSO.So it realy comes down to the task. When troubleshooting a mixed mode design, like e.g. a discrete precision ADC, the correlation between analog and digital matters and the MSO is the obvious choice.When debugging a purely digital circuit, including the decoding of some exotic protocol, the LA is right tool.With regard to screen space and UI when dealing with lots of channels, there are also USB-MSOs which can provide the best of both worlds in one instrument for certain tasks. There are more bus decoders than on the average MSO – but still not nearly as many as on a LA – and the number of digital channels is still limited to 16.

author: TiN
author_rank: Super Contributor
timestamp: July 28, 2016, 02:38:15 pm
content: Where is option for real LA?Very few USB LA's offer state and synchronous analysis mode.Tek page explains this bit further.D3f1ant example is a great one, showing lack of this mode in both MSO and USB LA's, requiring gigabytes of useless samples to capture that short "event", while even 30 year old HP or Tek TLA714 can easily capture samples only when you need them, and wait for trigger on anything you don't need.

author: jjoonathan
author_rank: Frequent Contributor
timestamp: July 28, 2016, 03:42:59 pm
content: Quote from: TiN on July 28, 2016, 02:38:15 pmIf you need it you need it, but the price of a LA with state machine triggers buys a lot of DRAM.

author: tautech
author_rank: Super Contributor
timestamp: July 28, 2016, 03:54:03 pm
content: And of course the memory depth of any MSO need be taken into account, they are each vastly different.Siglent SDS2000X series MSO:16 Ch14Mpts/CHDatasheet:http://www.siglentamerica.com/USA_website_2014/Documents/DataSheet/SDS2000X_DataSheet.pdf

author: Fungus
author_rank: Super Contributor
timestamp: July 28, 2016, 03:58:18 pm
content: What's the budget for the "MSO"?Doesn't it depend an awful lot on how much the MSO costs?

author: Berni
author_rank: Super Contributor
timestamp: July 28, 2016, 04:14:42 pm
content: Quote from: Fungus on July 28, 2016, 03:58:18 pmAlso a good point, my MSO9000 has 1Gpt of memory and can sample at up to 10GS/s on digital but I never used all of the avalable memory.EDIT: sorry I mean 128 Mbit up to 2GS/s for digital channels

author: jjoonathan
author_rank: Frequent Contributor
timestamp: July 28, 2016, 04:31:59 pm
content: Quote from: Fungus on July 28, 2016, 03:58:18 pmWherever I look I look the price is always the same: "Call Us"EDIT: Well, it's either "Call Us" or "I got one for (statistically improbable price) on ebay!"

author: tautech
author_rank: Super Contributor
timestamp: July 28, 2016, 04:35:39 pm
content: Quote from: Berni on July 28, 2016, 04:14:42 pmNot quite, you're quotingOption 500analog specs:From the Datasheet:Acquisition: digital channelsMaximum real time sample rate 2 GSa/sMaximum memory depth per channel 128/ 64 Mpts with 2 GSa/s. 64/32 Mpts with sampling < 2 GSa/s (single/repetitive mode).

author: Fungus
author_rank: Super Contributor
timestamp: July 28, 2016, 04:55:30 pm
content: Quote from: Berni on July 28, 2016, 04:14:42 pmSo... don't keep us in suspense! How much do they cost?

author: Berni
author_rank: Super Contributor
timestamp: July 28, 2016, 04:58:41 pm
content: Ah my mistake sorry. This shows how much use the MSO feature sees on my side. But I'm sure someone else out there couldn't live without the analog and digital correlation benefits of it.

author: Berni
author_rank: Super Contributor
timestamp: July 28, 2016, 05:13:34 pm
content: Quote from: Fungus on July 28, 2016, 04:55:30 pmIt goes in to the "I got it on eBay for A improbably low price" bin. I bought it from Keysights eBay store as a DSO9254H because they got discontinues for spot on 6 grand. Later on trough software turned it in to a MSO9404A with all options unlocked. It appears to be made in 2012 and had only been used for about 3 months all together by looking at windows logs.Edit: Before anyone asks no it's not software upgradable to 4GHz, The 2.5GHz In the H version is the 4 GHz in the A version by hardware. The software downsampling used to get the 10 bit resolution limits it to 2,5GHz

author: nctnico
author_rank: Super Contributor
timestamp: July 28, 2016, 09:35:54 pm
content: I have both an MSO and logic analyser (Tektronix TLA715 + 32Mpt 8Gs/s acquisition module). For debugging digital circuits I usually just use the TLA715. In the past I have used an MSO for debugging FPGAs but even though an MSO works for 99% of the logic analysis tasks the logic analyser still wins due to it's triggering and selective recording capabilities.

author: aandrew
author_rank: Frequent Contributor
timestamp: July 29, 2016, 02:17:19 am
content: I've got both; I use either Saleae or sigrok firmware on my USB LA depending on what I'm trying to do (being able to capture and manipulate over an ssh connection via remote is worth learning how to use sigrok). The logic analyzer in my MSO (MSO5074FG) is iffy at best, but it wasn't purchased for its LA; it was purchased because it's a cheap, hackable scope that just happens to have a kind of shitty LA and FG bolted on. If the LA and DSO sides were better synchronized and it had *some* triggering ability beyond the basics I'd use it a hell of a lot more, but as it is I like sigrok and the USB LA.

author: rs20
author_rank: Super Contributor
timestamp: July 29, 2016, 02:27:04 am
content: When using a borrowed USB LA for the first time, I was absolutely astonished to discover that the LAcould notbe configured to display a live stream of SPI data on my screen. I had an accelerometer taking measurements, and I just wanted to see them live, on screen, in response to me manipulating the sensor. I started a thread on this forum somewhere, and it was quickly pointed out to me that this "is not the point"/"is not the intended use" of USB LAs.But I just can't get my head around this fact, given that it would betrivialfor them to support this functionality. I accept that this is the way that LA's are, apparently, but still find it deeply difficult to understand. It's for this reason that I bought an USB MSO* in preference to a USB LA.* Don't worry, I have a real display-and-knobs DSO as well, but a USB MSO seemed like a reasonable second purchase, especially as I have need of collecting lots of analogue data to disk.

author: LabSpokane
author_rank: Super Contributor
timestamp: July 29, 2016, 04:41:19 am
content: Quote from: rs20 on July 29, 2016, 02:27:04 amSomeone correct me, but I believe low-end USB LAs of the Saleae variety (what I have) don't decode in hardware. They actually are directly sampling and storing samples of the waveforms and can only store in computer RAM. This is done for acquisition speed reasons. I don't think changing this is trivial, at least not on a $150 USB LA.Keysight (and others?) decode in hardware, and that makes live streams practical.

author: Berni
author_rank: Super Contributor
timestamp: July 29, 2016, 05:50:17 am
content: Yes the Saleae is very simple in terms of hardware. The older 8 bit ones contain only one chip inside. It is a MCU with built in USB that uses a DMA to barf the contents of an IO port register out of it as quickly as it can. The PC side software then does all the smarts of waveform compression, ram as sample memory and any decoding. Newer ones have a chip or two more to allow for faster sample rates and analog channels but that's about it. I love having essentially unlimited sample monody.

author: Sal Ammoniac
author_rank: Super Contributor
timestamp: July 29, 2016, 06:01:47 pm
content: Quote from: Berni on July 29, 2016, 05:50:17 amIn the case of the Saleae it's not the limited hardware that bothers me. That's to be expected given the price. It's the Windows application that is lacking. It doesn't even support such basic logic analyzer functions such as grouping multiple signals together into a bus. If I have, say, four signals I'm using as state output, I'd like to be able to group them and read the state as a decimal number on the display rather than having to decode four separate lines as binary and combine them in my head. I could go on and on, but it's clear that they have been very slow to add features LA veterans have come to expect in a LA.

author: pascal_sweden
author_rank: Super Contributor
timestamp: July 29, 2016, 06:16:33 pm
content: That's interesting to hear about the software of the Saleae. I though that the software was their only selling point... and now I hear that their software is no good.Some people buy a Chinese rip-off and use the Saleae software for all its goodnessSo the software isn't something to write home about? =)

author: rs20
author_rank: Super Contributor
timestamp: July 29, 2016, 06:23:15 pm
content: Quote from: LabSpokane on July 29, 2016, 04:41:19 amAnyone please correct me too!The LA has an "infinite " (i.e. hard-drive-backed) memory capability, which means that the hardware is streaming data to the software. Since the computer software is taking the data and dumping it to the hard drive, there's nothing stopping them (apart from laziness) from doing SPI decoding in parallel atsomeclock speed. Maybe hardware is beneficial at extremely high clock speeds, but to say that the hardware is totally incapable is indeed wrong. It's could just be a software feature which works with the current hardware, at least for modest clock rates.Alternatively, making the tiny change to the hardware that it can re-arm its own trigger, and thus send a stream of little blocks of data, makes it even easier for the software to handle. It could be much like the SPI decoding on Rigol scopes -- when the trigger rate gets too high, the SPI decoding can't translate every waveform that comes through. But Rigol (and others with no hardware decoding support) still provide the feature, since it's still hugely valuable even if it only displays a subset of SPI packets, and because it works perfectly at lower data rates too. Just blanket banning continuous triggering is really just cutting corners in software and firmware, and indefensible from a hardware feasibility standpoint AFAICT.

author: nctnico
author_rank: Super Contributor
timestamp: July 29, 2016, 06:47:34 pm
content: Quote from: LabSpokane on July 29, 2016, 04:41:19 amAFAIK a logic analyser has never been about showing live streams and I don't know of any logic analyser which can show live streams at a decent speed. A logic analyser has always been about capturing signals and analysing them afterwards. At least that is how I have always been using them.

author: rs20
author_rank: Super Contributor
timestamp: July 29, 2016, 07:10:16 pm
content: Quote from: nctnico on July 29, 2016, 06:47:34 pmYou appear to be correct, the general consensus is exactly that, not a terribly satisfying argument: "LA's don't show live data because that's not what LA's do". Which is why I don't want a logic analyser. What I want is a USB MSO minus the analog channels; but as far as I can tell, such a thing doesn't exist because people will tell you "that's a logic analyzer"*, but then if you get a logic analyzer, you lose the live monitoring functionality that is so central to many debugging workflows. I just can't get my head around why people are happy with this state of affairs, but evidently my workflows are wrong and I should feel bad.* And so what I got was a USB MSOwiththe analog channels, and I would be strongly tempted to do so even if I did purely digital work!?

author: Berni
author_rank: Super Contributor
timestamp: July 29, 2016, 07:48:43 pm
content: Yes such a thing is only a software feature. The SPI decode is so fast that it could run in real time. You could run the hardware in continuous capture mode since triggering is also done on the PC side.Saleae is not the best out there, but the basic features that it has work very well and you can get knockoff hardware for it very cheaply.If you need a real big boy LA then you will know you need one. But most of you out there won't ever need it.(I never have)

author: nctnico
author_rank: Super Contributor
timestamp: July 29, 2016, 08:04:26 pm
content: Quote from: Berni on July 29, 2016, 07:48:43 pmBut even then you have to ask yourself what the actual value is of such a feature. I have an Agilent MSO and the decoded serial data usually changes so fast that the only thing you notice are the numbers changing. You can't tell whether the numbers are right or wrong (and just forget about spotting an anomaly).

author: rs20
author_rank: Super Contributor
timestamp: July 29, 2016, 08:16:11 pm
content: Quote from: nctnico on July 29, 2016, 08:04:26 pmHow about seeing live feedback and checking for correlation between the real world and the measurements on screen -- gyroscope, accelerometers, light sensors, ADCs reading DC values... USB lines in response to different keystrokes. Low data rate applications like clap sensors. I mean really, just try to contrive any situation in which an SPI line produces small amounts of sporadic data, OR even large amounts of highly repeatably structured data. Also, set up a glitch filter/trigger of some sort, and manipulate the device to see exactly when glitches occur.It may well be true that the serial lines thatyouinteract with are carrying huge numbers of bytes per second, or unstructured data that requires deep interpretation. But since when were test instruments about focussing on one use case at the exclusion of all others? It's crazy to take a discussion the LA's should have this feature and flip it into an assertion that even MSO's shouldn't, especially when most MSOs provide it and some even provideASICimplementations for even more speed. Seems like an awful load of bother to go to for a feature of no "actual value".

author: tautech
author_rank: Super Contributor
timestamp: July 29, 2016, 09:08:00 pm
content: While LA's might haveunlimitedstorage and that being their great advantage isn't the MSO's trigger suite the work around to compensate for lack of a large memory. Sure one has to be somewhat intimate with the data stream to know where to inspect the stream. Or is it just too hard?Who uses: Window, Interval, Dropout, Runt or Pattern triggers?Each of which contain subsets of parameters to further refine what are quite standard additional trigger types in a DSO, nevermind an MSO.Then there's the sets of Decode triggers, each with further subsets of user definable conditions, so many so that how can you not find what you seek?Segmented memory and History capable DSO's.Are these other features that are under utilised?Can we liken advanced scope use to driving an auto shift car compared to an 18sp Roadranger truck box, the RR just takes practice.....lots.

author: LabSpokane
author_rank: Super Contributor
timestamp: July 29, 2016, 09:54:58 pm
content: Quote from: nctnico on July 29, 2016, 06:47:34 pmYes. I should have qualified "live." The scope is easier to capture and view a recent data stream than a USB logic analyzer. But that's it. You're absolutely correct that neither is live and only captures for later analysis.

author: free_electron
author_rank: Super Contributor
timestamp: July 29, 2016, 11:56:11 pm
content: MSO or Scope synced to a real logic analyser ( like syncing an infiniium to a 16902 series )