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What to buy - Dedicated Logic Analyzer vs "The new Scopes" aka. SDS824/DHO924(S)

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kripton2035:
don't forget you can use sigrok app to connect to these scopes if they are connected to the same network
you will get a ton of protocols decoders, and more memory to store that signal.
more here : https://www.eevblog.com/forum/testgear/new-sigrokpulseview-hardware-support-(siglent-sds-hd-rigol-dho800-)/msg5555753/#msg5555753

Traceless:

--- Quote from: artag on November 28, 2024, 10:37:34 pm ---All these 'logic analysers' are a bit disappointing. They're not logic analysers at all, they're multichannel (for values of multi mostly in the range 8-16) 1-bit oscilloscopes. Some - especially the ones built into scopes - don't even have a proper trigger on the digital side. At best, a single word match. No clock input.

--- End quote ---


--- Quote from: 44kgk1lkf6u on November 29, 2024, 04:55:27 am ---Just like the other things that others said are not real logic analyzers, it seems to lack some features that I would expect a logic analyzer to provide.

Sampling on a clock input.  This means the X axis will be clock cycles instead of time.  I find it easier to read a screen when each line is a data transmission than when I have to scroll to find the clock signal switching and then look at what the data signals are.  It also means the max sample rate and the max sample duration are available at the same time.

Only storing changes.  Another way to avoid having to choose between sample rate and duration.

A programmable trigger state machine.  For example triggering when a sequence of words are transferred on a parallel bus following another sequence of words being transferred on another bus within a certain delay.

Also note that a logic analyzer that has these features may lack some features such as decoding SPI.

--- End quote ---

I see that the missing trigger feature is a weakness. But since both the scopes and the Saleae logic probe suffer the same weakness I'd call it a tie between the dedicated probe and the scopes in that regard. That being said in the thread that kripton2035 linked there is a screenshot of the sigrok application showing a capture of the 16 data channels on the Siglent scope overlayed with the scope's channel 1, in the bottom right corner there is a box "Trigger C1 DC".
Does that mean I could use the analog input channel of the scope to trigger on a clock signal for the logic probe or is this just an unrelated overlay?

Are there any logic analyzer options with capabilities similar to the Saleae that would provide the missing trigger feature? I mean sure a Keysight 16861A would probably be a nice device but a) its probably massive overkill for my applications and b) if the only price you can find is "get an offer" on the Keysight website that usually means you can probably sell your car and/or your house and still not have enough money to afford the device ;) (Note: I'm in the EU, so used, reasonably priced Keithley/HP gear that is not a complete basket case is basically unobtainium)


--- Quote from: ebastler on November 29, 2024, 07:06:06 am ---If you are specifically interested in using the digital channels, I'd say the answer is yes.

The SDS8..X HD has a more generous 2 GSa/s to begin with. The optional logic probe comprises its own sampling subsystem in the external unit. Which implies some limitations (e.g. no mixed-signal triggering), but also means that you get 1 GSa/s for the digital channels without affecting the analog sampling rate at all.

--- End quote ---

Okay based on that observation plus what I've read on other threads and the comments of ataradov and 2N3055 about the DHO924 I can definitely rule out the Rigol already. So the race is between Saleae and Siglent SDS 824 + SLA1016.


--- Quote from: ebastler on November 29, 2024, 07:06:06 am ---In general, a dedicated PC-based logic analyser will give you more screen space, a more tailored UI, more signal decoder options. The built-in logic analyzers in the scopes will make it easy to view and correlate analog and digital signals. I'd say it depends on your application which solution works best.

--- End quote ---

IIRC you can hook up the new scopes to an external monitor via HDMI, or see the display content via a Desktop application, which would at least solve the screen real estate problem.


--- Quote from: ebastler on November 29, 2024, 07:06:06 am ---However, when you state that the Salea logic analysers are "at a similar price point" as the entry-level 12 bit scopes, that can only refer to Salea's most basic "Logic 8" -- only 8 channels and 100 MSa/s. Again, it depends on your application whether that's enough. There are B-brand alternatives with better hardware performance, e.g. the DSLogic series from DreamSourceLabs, although with less refined software.

--- End quote ---

Well maybe I was using the term "similar" to liberal here. The Siglent SDS824 + SLA1016 costs somwhere around 1100-1200€, the Saleae 1700-1800€. Since a good instrument is pretty much a one time purchase I consider that to be still in the same ballpark aka. "similar".  As a counter example the Keysight 16861A is not available at a "similar" price point with high likelihood ;)

btest:
(My first post!)

I've been doing embedded software for going on 30 years now and my needs have definitely changed over the years. I own an Agilent 16903A logic analyzer that I haven't turned on in years. I also own a Saleae that I haven't taken out of its case in years. It comes down to what are you trying to look at. If you are trying to analyze the handshake between 2 devices use a PC based logic analyzer. if you are trying to look at signal integrity (eye diagram, noise, jitter) then you will need a scope. At the end of the day you probably need both. And I have never found a scope that had actually useful logic channels. The ones I tried in the past could only do serial decode on the analog channels - go figure. Not sure how true that is today.

The instrument I go to most lately is a DreamSource DSLogic U3pro16. With it I can sample at high rates and get long (10+ minutes or more) captures of serial data. I2C, SPI, UART and lately a lot of CAN. It's real easy to scroll through the data or it can be exported. If you use buffer mode it has multi-stage triggering. The app is based on Sigrok and is open source. It's the depth of capture that makes these so valuable. Even the best scopes are limited as to memory depth while the DS just pushes the data over USB to your hard drive. One thing that is often not mentioned is the DS has terminated coax flying leads while analyzers like the Saleae is just a wire. It makes a difference, trust me, when you are looking at higher speed signals.

But there are times when a scope is your only answer. I have been debugging a CAN device that seems to lose arbitration with itself as it is the only device transmitting on the bus. It sends out a handful of bits, stops and then immediately retries the message. While this event is visible on the DS it does not have the ability to trigger on Start-Of-Frame like my scope can so you spend a lot of time looking for it in the data. The ability to trigger on SOF is also important to do things like generate an eye diagram. That being said, if I were buying a scope making sure it had all the licenses necessary for protocol decoding and analysis would be my first priority.

ebastler:

--- Quote from: Traceless on November 29, 2024, 08:49:37 am ---Well maybe I was using the term "similar" to liberal here. The Siglent SDS824 + SLA1016 costs somwhere around 1100-1200€, the Saleae 1700-1800€. Since a good instrument is pretty much a one time purchase I consider that to be still in the same ballpark aka. "similar".  As a counter example the Keysight 16861A is not available at a "similar" price point with high likelihood ;)

--- End quote ---

But even the top-model Saleae (Logic Pro 16) gives you very limited analog capabilities: 50 MSa/s max., and no analog probes included at all. So you should really compare to to a combination of SDS804X HD + SLA1016, which comes at half the price of the Logic Pro 16. Or maybe a combination of SDS8..X HD and a DSLogic U3pro16 or similar?


--- Quote ---IIRC you can hook up the new scopes to an external monitor via HDMI, or see the display content via a Desktop application, which would at least solve the screen real estate problem.
--- End quote ---

The Siglent scope does not have an HDMI output, but you can use the web interface to view the screen (and drive the scope via the mouse or touch) from a web browser. The update rate is reduced vs. the built-in screen, but it is certainly usable. But since the UI was designed to work with the small screen, it is still a bit limited compared to Saleae or similar logic analyzer software which was designed for a large monitor from the start. 

Edit: Typos...

tggzzz:

--- Quote from: btest on November 29, 2024, 08:55:45 am ---(My first post!)

I've been doing embedded software for going on 30 years now and my needs have definitely changed over the years. I own an Agilent 16903A logic analyzer that I haven't turned on in years. I also own a Saleae that I haven't taken out of its case in years. It comes down to what are you trying to look at. If you are trying to analyze the handshake between 2 devices use a PC based logic analyzer. if you are trying to look at signal integrity (eye diagram, noise, jitter) then you will need a scope. At the end of the day you probably need both.

--- End quote ---

Welcome to the forum :)

Those points are very valid. Unfortunately too many people don't understand the distinction between analogue waveforms (e.g. TTL/CMOS/etc) and digital signals.  Use the analogue domain tool to verify and validate analogue signals, then flip to the digital domain and use digital domain tools to verify and validate digital signals.


--- Quote ---And I have never found a scope that had actually useful logic channels. The ones I tried in the past could only do serial decode on the analog channels - go figure. Not sure how true that is today.

The instrument I go to most lately is a DreamSource DSLogic U3pro16. With it I can sample at high rates and get long (10+ minutes or more) captures of serial data. I2C, SPI, UART and lately a lot of CAN. It's real easy to scroll through the data or it can be exported. If you use buffer mode it has multi-stage triggering. The app is based on Sigrok and is open source. It's the depth of capture that makes these so valuable. Even the best scopes are limited as to memory depth while the DS just pushes the data over USB to your hard drive. One thing that is often not mentioned is the DS has terminated coax flying leads while analyzers like the Saleae is just a wire. It makes a difference, trust me, when you are looking at higher speed signals.

But there are times when a scope is your only answer. I have been debugging a CAN device that seems to lose arbitration with itself as it is the only device transmitting on the bus. It sends out a handful of bits, stops and then immediately retries the message. While this event is visible on the DS it does not have the ability to trigger on Start-Of-Frame like my scope can so you spend a lot of time looking for it in the data. The ability to trigger on SOF is also important to do things like generate an eye diagram. That being said, if I were buying a scope making sure it had all the licenses necessary for protocol decoding and analysis would be my first priority.

--- End quote ---

My preference is to have two tools each of which is good at one job, rather than one tool that is poor at two jobs. Of course that implies knowing what "the job" entails; for digital signals to sort the wheat from the chaff you need good filtering and triggering.

The one area where a single tool might be more capable is where it is necessary to have an analogue signal trigger the digital tool, or a digital signal trigger the analogue tool. However, the limitations of a specific tool might make that impractical, and skill and imagination might mean it can be achieved with two separate tools. The only way to assess that is to define a use case, then carefully read and understand the user manuals (not the datasheets!).

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