How many channels do I need to decode any serial interface with oscilloscope? - Page 1
Forum section: electronics / beginners

author: caveleira
author_rank: Newbie
timestamp: July 20, 2016, 01:08:05 pm
content: Hi, I am considering to buy an oscilloscope for our Company. Not sure yet exactly what for, and nothing too expensive.What for sure seems interesting is the possibility of Decoding Serial Interfaces. Since 4 Channels is quite more expensive than 2, comes the question, how many channels do I Need? SPI for example uses 4 lines, means that the oscilloscope Needs the four channels attached to decode the data? Makes sense, but is not yet so well informed by the manufacturers. So hope someone can hier clarify me that.Thanks in advance!

author: Kalvin
author_rank: Super Contributor
timestamp: July 20, 2016, 01:21:13 pm
content: You may also consider Saleae Logic-products in addition to the oscilloscope. The Saleae Logic-products are very handy and can really save your day. There might be some other similar products in the market, but I have used the Saleae Logic-devices in my professional life with great success.

author: MosherIV
author_rank: Super Contributor
timestamp: July 20, 2016, 01:22:36 pm
content: Most oscilloscopes do not allow you to decode serial interfaces on the analogue channels.(Some do but you have to check the individual oscilloscope features and then they are software enabled add ons, ie more moeny).What you are talking about is a Mixed Signal Oscilloscope, where they have 2/4 analogue channels and 8/16/24/32 digital channels.Again, the serial decode will likely be software enabled add on.

author: caveleira
author_rank: Newbie
timestamp: July 20, 2016, 01:43:21 pm
content: Quote from: Kalvin on July 20, 2016, 01:21:13 pmno thanks, I want all in one PieceQuote from: MosherIV on July 20, 2016, 01:22:36 pmwell, the ones im looking at, they can decode, and they are not MSO.Of course Im thinking buying also the Serial decode Software.The question is still.. can the Software decode with 2 channels, or Need 4.

author: dmills
author_rank: Super Contributor
timestamp: July 20, 2016, 01:45:59 pm
content: SPI needs at least 3, and 4 if you want to watch both directions, UART can of course make do with 2 as can I2C.Regards, Dan.

author: Kilrah
author_rank: Unknown
timestamp: July 20, 2016, 01:46:25 pm
content: Well obviously you need as many channels as the particular interface you want to decode has lines... so that's only one for one-wire, SPI needs 4 and others may need more.Quote from: caveleira on July 20, 2016, 01:43:21 pmDon't know your reasons, but in most cases a standalone PC-based logic analyzer is more useful than the same feature built in to a scope.

author: caveleira
author_rank: Newbie
timestamp: July 20, 2016, 01:56:05 pm
content: thank you very much dmills, now is clarifiedQuote from: Kilrah on July 20, 2016, 01:46:25 pmthanks to you tooPD:because of the work Environment, no PC

author: tszaboo
author_rank: Super Contributor
timestamp: July 20, 2016, 01:57:07 pm
content: Get a 4 channel MSO with built in 16 channel Logic analiser. Saleeaeie is a toy, with other USB logic analisers you lose time instead of working.

author: MosherIV
author_rank: Super Contributor
timestamp: July 20, 2016, 02:01:22 pm
content: QuoteTo decode SPI, you must have 4 channels, you can get away with 3 if you are not bothered about the ChipSelect.4 Channel DSO are way more expensive than 2 channel ones, probably because the low end 2 channel models are targeted for hobbiests but the 4 channel models are targeted for companies.A compromised would be a Mixed Signal Oscilloscope with 2 analogue channels and 8/16 digital channels. I do not know if any vendor does one of these today, I have certainly used one that was a HP that was nearly 20 years old. Hopefully, this will be a cheaper option that the 4 channel DSO but I do not know.

author: wraper
author_rank: Unknown
timestamp: July 20, 2016, 02:07:16 pm
content: Quote from: MosherIV on July 20, 2016, 02:01:22 pmcertainly not

author: suicidaleggroll
author_rank: Super Contributor
timestamp: July 20, 2016, 02:58:33 pm
content: Quote from: caveleira on July 20, 2016, 01:56:05 pmYou're developing and/or debugging a serial interface and you don't have access to a computer? How does that work?I'm struggling to think of an application in which you would need to decode a serial data stream, but you wouldn't have a computer there with which you could actuallydo somethingwith the information you learn from the LA.

author: Aeternam
author_rank: Unknown
timestamp: July 20, 2016, 02:59:01 pm
content: Quote from: MosherIV on July 20, 2016, 02:01:22 pmThe new R&S HMO1002 fits the bill:https://www.rohde-schwarz.com/product/hmo1002-productstartpage_63493-61541.htmlI believe Dave did review and tear down videos not too long ago.Be aware though that you'll need (a) the serial bus decode option and (b) the optional digital probe.

author: caveleira
author_rank: Newbie
timestamp: July 20, 2016, 04:05:02 pm
content: Quote from: suicidaleggroll on July 20, 2016, 02:58:33 pmThis should be a multipurpose tool. Sometimes there will be PC, sometimes not.Thats all about this topic my friends, I already have info from oscilloscopes and so on, thanks for your help.

author: Nozzer
author_rank: Contributor
timestamp: July 20, 2016, 04:21:19 pm
content: Quote from: Aeternam on July 20, 2016, 02:59:01 pmThe newer HMO12nn series offer it too. I was reading their manual (available online) and it suggests that if you buy their full software option you get the 8 digital channels on the POD plus three analogue channels on their two channel scope. Apparently the output for the built-in 25KHz signal generator serves as the third analogue input. This is interesting as the HMO2024 which I was considering and has 4 analogue channels only offers 3 usable analogue channels despite having 4.

author: tautech
author_rank: Super Contributor
timestamp: July 20, 2016, 04:51:46 pm
content: Quote from: caveleira on July 20, 2016, 01:43:21 pm.Some protocols do require more than 2 channels and as others have described if you need to see all the related signals you'll want 4.Additional digital channels to 2 analogue channels in that case may be a cheaper option, the Siglent SDS1000X or plus series with 16 ch La and Decode might interest you.http://www.siglenteu.com/pdxx.aspx?id=2373&T=2&tid=1If you drill down into the accessories tab you'll see the LA has a wide flat ribbon cable that can be a little inflexible however ASAIK it can be substituted with an SCPI cable that is more flexible.A SDS2000X series on the other hand is available in 2 or 4 ch versions and a 16 ch LA option can be added if required, it's a nicer unit with the LA cable, while still a flat cable is split into 2 x 8 channel cables with a detachable pod on the end of each cable that is ~1m long.The second image in this page gives you an idea of what it looks like:http://www.siglenteu.com/pdxx.aspx?id=1195&T=2&tid=1There's some upgrade deals on these ATM that might be worth considering.There's also the option of using the external trigger input that both these Siglent models provide for a de facto 3rd channel.

author: tszaboo
author_rank: Super Contributor
timestamp: July 20, 2016, 05:00:53 pm
content: Quote from: tautech on July 20, 2016, 04:51:46 pmIt is for a company. You dont suggest chinatech scopes for a company. You buy an Agilent, R&S, or LeCroy based on taste, or Tektronics if you are a clueless manager.

author: wraper
author_rank: Unknown
timestamp: July 20, 2016, 05:25:18 pm
content: As nothing too expensive asked, and likely cannot be cracked as for the company, then 4 ch GW Instek GDS-2000E series 4ch scope might fit. Serial decoders come by default, no options to purchase or crack, everything already there.

author: LabSpokane
author_rank: Super Contributor
timestamp: July 20, 2016, 05:52:37 pm
content: Quote from: Kilrah on July 20, 2016, 01:46:25 pmYup. You need the scope when looking for signal integrity issues and the decoded data. For pure decode, a separate device is more useful.In Keysight's line, it's worth being aware the decoding is supported on the MSO lines on the 3000 series and above scopes. Never mind that the 2000 series has logic probes.

author: tautech
author_rank: Super Contributor
timestamp: July 20, 2016, 05:54:52 pm
content: Quote from: NANDBlog on July 20, 2016, 05:00:53 pmTell that to my company customers.

author: vodka
author_rank: Frequent Contributor
timestamp: July 20, 2016, 05:59:19 pm
content: QuoteI think that the caveleira corporation is a little corporation i doubt that they can spend on expensive instruments as Tektronicks or Agilent

author: vodka
author_rank: Frequent Contributor
timestamp: July 20, 2016, 06:16:10 pm
content: Quote from: tautech on July 20, 2016, 05:54:52 pmThe problem is that the Agilent , Lecroys etc instruments are manufactured in China as the Siglent and Rigol, but 4 or 5 times more expensives.Now if the instruments traditional corporation want to sell, they know that they must do.

author: JPortici
author_rank: Super Contributor
timestamp: July 20, 2016, 07:19:58 pm
content: chinatech doesn't mean "made in china"that would be stupid.

author: Nozzer
author_rank: Contributor
timestamp: July 20, 2016, 07:23:38 pm
content: Quote from: vodka on July 20, 2016, 06:16:10 pmThe new Rohde and Schwartz are manufactured in the Czech Republic under strict German supervision. The HMO1202 100MHz version sells for under £700 (before tax) in the UK and a little under £1500 for the 300 MHz version. The external digital probe and software will add around an extra £600 to that figure. The downside is that it only offers 10,000 wfs.

author: vodka
author_rank: Frequent Contributor
timestamp: July 20, 2016, 08:39:21 pm
content: QuoteI see the oscilloscope series HMO1202 prices any low from 1000€ (exclude VAT) . Besides ,i compare among the oficial house and distribuitor and the price are the sameSpanish Rohdehttp://shop.rohde-schwarz.com/es/catalogsearch/result/index/?dir=asc&limit=25&order=price&q=hmoGerman Rohdehttp://shop.rohde-schwarz.com/de/catalogsearch/result/index/?dir=asc&limit=25&order=name&q=HMOSpanish Farnellhttp://es.farnell.com/webapp/wcs/stores/servlet/Search?catalogId=15001&langId=-5&storeId=10176&categoryId=700000027009&eq=N%3D220630%26amp%3BNs%3DP_STORE_MARKETING_RANK_FARNELL_ES%257c0%257c%257cP_MAN_PART_NUM%257c0%26amp%3BNtpc%3D1%26amp%3BNtpr%3D1&showResults=true&aa=true&pf=513163562&vw=And testing the manufactured placehttps://en.wikipedia.org/wiki/Rohde_%26_Schwarz

author: danadak
author_rank: Super Contributor
timestamp: July 21, 2016, 09:21:22 am
content: You said cost was a consideration, then discussed no PC.If you get a PC, which you need to debug unless you are using stand alone board withdisplay, these are very low cost, most serial busses -http://www.ebay.com/itm/24MHz-8-Channel-USB-Logic-Analyzer-8-CH-Logic-Analyzer-for-Arduino-MCU-/191685084604?hash=item2ca15245bc:g:KFYAAOSwyQtV1vOORegards, Dana.

author: Galenbo
author_rank: Super Contributor
timestamp: July 22, 2016, 02:53:53 pm
content: Quote from: caveleira on July 20, 2016, 01:08:05 pmI am currently working on an SPI (=serial) problem, and it's more parallel than you think.I try to connect 3 different modules (ETH, GLCD, MCP) on the same SPI "port" of a PIC processor, the way it's theoretically described for ages in every book. Mosi, Miso, Clock. Finished.in practice:-every SPI module needs his own CS_EN pin.-to rule out problems and easy time-based debug, I chose to give every module temporarily it's own RST pin.-for some reason, the GLCD has an AO pin: data or command. You can drive the backlight led with pwm.-the ETH and MCP module can give feedback on an interrupt pin.-to control start/stop sampling of the analyser, I control an output bit in my program on suspicious placesThis gives:3-clk, miso, mosi3-cs0 cs1 cs23-rst0 rst1 rst22-AO, led_pwm2-int0 int11-bit for start/stop analyser"only" 14 channels, to debug a "serial" protocol, witch I consider easy and basic. (and shitty)I have a 8-channel analyser witch is enough for this, but less is really not workable.Quote from: Kalvin on July 20, 2016, 01:21:13 pm+1, due to their "sold out" at the time I bought the cheapest $10 replica, that device seems to replace everything in the -y2010 -500$ market.After this experiences, I would never choose a scope with integrated analyser, except maybe a $10K scope with a $4K analyser, for a $50BN project, witch is far away from my abilities and needs at the moment.The only need to get it integrated I see at the moment is the ability to see synchronisation between analog and digital, but in my accuracy and frequency range this can easily be done by triggering one device with the other, or record 1 channel with both devices the same time.

author: Galenbo
author_rank: Super Contributor
timestamp: July 22, 2016, 03:22:18 pm
content: Quote from: NANDBlog on July 20, 2016, 01:57:07 pmPlease enlight me on this.-What I donotmean: You are wrong, I do not agree, you know nothing,...-What I mean: Can you give me some personal examples and situations where you clearly saw the differences and where the better soft/hard where really worth the money? Where did the others fail or made you loose a day?

author: tszaboo
author_rank: Super Contributor
timestamp: July 22, 2016, 05:07:03 pm
content: Quote from: Galenbo on July 22, 2016, 03:22:18 pmI was working a lot with LAs when I was working with ADCs, switched front end. So if you dont see the analog signal, your conclusion was wrong. Also, you cannot quickly check that signal integrity is correct. The reason that the LA is connected to a system is 90% because something went wrong. Now, with an DSO, you dont usually have enought channels or capabilities to trigger correctly on a bit error, or CAN error frame or anything like, with an USB LA you cannot see what is causing the issue. I had this with digital isolators. The USB LA told me that everything is fine, when in reality, it was signals from the glitchland. When you need a USB LA or a MSO... There might be a very fine line. I think it is better to spend the company's money on something that I'm sure will do the job, than on something that "might be enough".And take a look at the list prices (farnell) for scopes, like the MSOX3024T (personal opinion to be minimum for electronics related work at the workplace). It is the same price as the DSOX3024T. But check other price. DPO2024B and MSO2024B has 600 EUR difference. It is hardly justifiable to buy just a DSO for work these days.

author: suicidaleggroll
author_rank: Super Contributor
timestamp: July 22, 2016, 05:14:07 pm
content: FYI - the newer Saleae models also do analog sampling. It only runs at 50 MSps so it can't do high speed lines, but it's more than enough to check for signal integrity on I2C, UART, CAN, and other <5 MHz digital signals.

author: JPortici
author_rank: Super Contributor
timestamp: July 22, 2016, 05:44:49 pm
content: SPI is shitty?not really.it's dead simple.it can be goddamn fast.itrather easy to make automated transfert with dma or internal buffers and the right peripheral.there are not all simultaneously verified for many other of the popular transfer methods. the downside is that you need a separate chip select line for each peripheral, i'll give you that(hint to reduce number of pins: demux with inverted outputs and enable)+1 for a MSO, get a proper tool. I would use a LA only if i had to check differential lines or a parallel bus or i have to keep track of more than 2 analog channels, otherwise i always use the analog channels and the decoder, i need to see what the hell is really going on, not ones and zeros.and even in that case the keysight 3000 would be the starting point, an instrument one can trust with only an hint of skepticism.another one i would pick is the picoscope because the advanced triggering comes out of the box.. that's the one i use at work, at the time it was the only scope that offered SENT decoding without asking for your future son and grandson as a collateral.. by the way, how good is the GWI GDS2000A Series logic analyzer?

author: Kilrah
author_rank: Unknown
timestamp: July 22, 2016, 07:03:20 pm
content: Quote from: NANDBlog on July 22, 2016, 05:07:03 pmSo you had a particular application where an USB LA was not enough, fair enough, but that's no reason to say it's just "a toy".I've had a Saleae device for 5 years (and just bought a new one after it was stolen), and it's always done a perfectly fine job of letting me debug/analyze things at protocol-level which is what I typically need. When I have to debug logic signals I'll typically do a 5-min check with the scope to see if signal integrity is OK just in case, once confirmed I can forget about it and go on spend my couple of days of protocol coding/fixing for which a scope would just be unnecessary and excessively bulky.

author: Galenbo
author_rank: Super Contributor
timestamp: July 23, 2016, 01:07:51 am
content: Quote from: NANDBlog on July 22, 2016, 05:07:03 pmYou are clearly on a whole other level than me.But for checking signal integrity, what is the difference between me connecting my probe+LA and you connecting the probe+LA cable?Quote from: NANDBlog on July 22, 2016, 05:07:03 pmYou are right about the $4K scopes, it makes hardly a difference. The "leather option" is cheaper for a Mercedes than for a Lada.But for my 4ch $1K scope (2009), the price for a model including a LA was double.On top of that, I was somewhat scared the internal LA would be limited, not be upgradeable, difficult to control,... compared to a PC-based device.A disadvantage I have, is that my scope doesn't have a Pass/Fail output, to connect to my LA. The newer 1054Z has this on the back.But the topic starter seems to have his reason for not wanting a PC-based LA.Maybe the Topic starter can say what the budget for 1 MSO scope is?