How to synchronise two oscilloscopes - Page 1
Forum section: electronics / beginners

author: gb243
author_rank: Contributor
timestamp: July 08, 2022, 09:03:37 am
content: I want to get a high end scope with good performance and a large screen. I cannot afford this and pay the arm and leg for the various basic decode options. How would I use a cheaper scope to decode an spi bus and have both scopes trigger at the same time. It looks like scopes have a trigger in only. My ideas.1. Build in a debug trigger pin in any design of mine Buffer it and take out to both scopes.2. Take the trigger pulse from 1 and feed via a pulse generator (Aim-TTI) which I can then delay the trigger from 5ns to 5s and then tune up and down to get to where I want to look. The 'tuning' will be a bit clunky (front panel VR) but better than nothing.I just cannot think of a way to get two scopes to talk to each other. Unless I am being stupid which as always is an option. No I do not want to hack a Rhode and Schwartz scope no matter how tempting.

author: Zero999
author_rank: Super Contributor
timestamp: July 08, 2022, 09:49:12 am
content: I don't see why you can't just connect the oscilloscope triggers together. Most oscilloscopes have the ability to delay taking data, after the actual trigger pulse. You could also invest in a timer counter, which can be useful for this kind of thing.

author: Ian.M
author_rank: Super Contributor
timestamp: July 08, 2022, 10:04:40 am
content: Some older CRO scopes had their timebase gate signals available on the rear panel so could easily be synchronised.However as you don't have that, use a scope *ONLY* to check the SPI signal integrity, then use a cheep Salae clone 'Logic 8' logic analyser, + Sigrok Pulseview software (FOSS) to decode the actual data.

author: Berni
author_rank: Super Contributor
timestamp: July 08, 2022, 10:10:46 am
content: You can simply connect each scopes to the same point on your board and have them trigger at the same time.Alternatively you can check if one of the scopes has a TrigOut BNC (Usually it is on the back). That port emits a pulse every time the scope triggers, so you can hook a BNC cable from that into the input of another scope to trigger from it. You will get a bit of extra delay in the triggering of the second scope since the signal has to go trough all this, but it should be a consistent amount of time, so you can just move the trigger point on the other scope some nanoseconds into the future to compensate.Note that it does depend how advanced of a trigger is usable with TrigOut. Edge triggers always work, but something like an advanced serial decode trigger or zone trigger might not work for this on some scopes (since some do these advanced triggering features in software)

author: gb243
author_rank: Contributor
timestamp: July 08, 2022, 11:46:33 am
content: Thanks for the reply. The issue is the scopes I have do not have a trig out. Neither does the couple of models I am looking at. If one did I would not have a problem. The only thing to do is experiment I guess.

author: gb243
author_rank: Contributor
timestamp: July 08, 2022, 03:25:47 pm
content: One scope I was looking at has an AUX Out. Apparently that means trigger out. Problem solved. For most people that may have been obvious. Never mind. Thanks again.

author: rstofer
author_rank: Super Contributor
timestamp: July 08, 2022, 03:31:49 pm
content: I sometimes create an artificial trigger signal and it could be fed to both scopes. Often this is done in software on a uC but I have done it with real hardware as well.It seems to me that decoding SPI would trigger with the negative going edge on the CS' signalI don't know what you are using for a scope but most analog scopes have two input channels and a separate non-displayed, trigger input.For a few bucks, you can get a logic analyzer that will probably work better because it will actually decode the data. Google around here for 'logic analyzer'. Like this:https://www.ebay.com/itm/124238666414Search around here for logic analyzer software.

author: JustMeHere
author_rank: Frequent Contributor
timestamp: July 11, 2022, 12:59:00 am
content: You can get away with only watching 2 signals for SPI. You don't need to monitor CS. You have to watch the data signals individually though. Trigger on the data signal. You can even get away woth probing both data signals together. This is because both chips seldom speak at the same time.

author: David Hess
author_rank: Super Contributor
timestamp: July 11, 2022, 04:16:28 am
content: Quote from: Berni on July 08, 2022, 10:10:46 amThat is the best option, because ...QuoteThe trigger output on these oscilloscopes is not a trigger output. It indicates when an acquisition happens and may have considerable jitter compared to the actual trigger, (1) unlike the gate output of an analog oscilloscope which will have a short but constant delay of 10s of nanoseconds. It can be used at lower sweep speeds where the difference does not matter.Besides the gate output of an old analog oscilloscope, some instruments like frequency counters may have a trigger recognizer output so the trigger in the frequency counter could be used to replace the trigger of an oscilloscope, and could drive multiple oscilloscopes, but this feature is not common even on old instruments.(1) For one thing, the FPGA clock which generates this signal is asynchronous to the trigger, but this is overshadowed by the pipelined FPGA logic which recognizes a trigger.

author: tggzzz
author_rank: Super Contributor
timestamp: July 11, 2022, 10:44:01 am
content: Quote from: Ian.M on July 08, 2022, 10:04:40 amThat is a sound debugging strategy, which beginners usually don't appreciate.It doesn't help when trying to correlate message contents with analogue waveforms.

author: Ian.M
author_rank: Super Contributor
timestamp: July 11, 2022, 10:57:18 am
content: Quote from: tggzzz on July 11, 2022, 10:44:01 amYes, there's no real substitute for a scope with enough channels or an integrated logic analyser when you need to do that in realtime.

author: RoGeorge
author_rank: Super Contributor
timestamp: July 11, 2022, 11:08:57 am
content: IIRC the latest Siglent oscilloscopes can do that, can synchronize multiple remote units to get upto 256 channels or so. Can not find the info right now, user 'tautech' might know more about what oscilloscope models can do that.

author: Huluvu
author_rank: Regular Contributor
timestamp: July 11, 2022, 11:23:22 am
content: The usb scopes from TiePie you can easily daisychain with some kind of hdmi cablehttps://www.tiepie.com/en

author: tautech
author_rank: Super Contributor
timestamp: July 12, 2022, 01:32:08 am
content: Quote from: RoGeorge on July 11, 2022, 11:08:57 amYep, these are a new headless DSO we are to see in the west Q3 this year however I don't believe they'll be cheap as even the entry level models are 500 MHz 4ch.512 channels is the limit but that needs 64 8ch units !You can read about them here:https://www.eevblog.com/forum/testgear/siglent-sds6000l-2ghz-12bit-8-ch-(china-only)/These apparently need some synchronizing but it appears to only be a common 10 MHz reference.