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| How does waveform updates on an oscilloscope work? Why do they work that way? |
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| pdenisowski:
--- Quote from: 2N3055 on April 18, 2023, 06:27:45 pm ---Trigger event is start of capture event, it cannot happen again until scope fills the whole requested time period + rearm time... --- End quote --- Yes. People sometimes forget that the waveform update rate may also be limited by the user settings: if you have 100 ms/div and 10 divisions, the maximum waveform update rate for any oscilloscope is < 1 waveform per second -- it will take 1 full second just to perform a single acquisition :) |
| ballsystemlord:
--- Quote from: 2N3055 on April 18, 2023, 06:27:45 pm --- --- Quote from: ballsystemlord on April 18, 2023, 04:41:40 pm ---<snip> It was also said, --- Quote from: JPortici --- The moment the analog signal is correct you should switch to a protocol analyzer (which can usually also put data on the bus, which makes it a much more useful trigger. Imagine doing CANbus analysis of a network with only an oscilloscope). --- End quote --- Which brings us to the most advanced part of the question, which I didn't think I'd ask. Now my own scope has 16 digital channels (MSO5074 LA). I was trying to save myself a few $$$ and buy a scope that could do protocol analysis, and it can, via the web interface. So, does the scope have blind time with it's digital channels so that I can't trigger on them at certain points during the capture? IDK. I'd ask rigol, but every question I've ever asked them has gone unanswered. I've tired email and phone without result. The phone just goes to a voice mail. --- End quote --- <snip> Reading your last paragraph I really don't understand what you mean... Scope waits for a trigger (analog, digital or serial protocol doesn't matter). After scope triggers (because trigger engine decides the conditions for trigger were fulfilled) scope grabs a certain time (as set with timebase ) of data on all enabled channels (analog and digital) and saves it into acquisition memory, notifies display engine and whatnot and resets itself for new capture and starts a new wait for next trigger. So minimum time between two triggers is captured time + this time scope needs for it to rearm trigger engine and gets ready for new trigger. This rearm time is blind time between two captures. So minimum time between two trigger events is going to be time set by timebase +blind time. Tigger event is start of capture event, it cannot happen again until scope fills the whole requested time period + rearm time... --- End quote --- I meant, are the digital channels treated any differently, with respect to triggering or to waveform updates per second? |
| 2N3055:
--- Quote from: ballsystemlord on April 18, 2023, 08:42:16 pm ---I meant, are the digital channels treated any differently, with respect to triggering or to waveform updates per second? --- End quote --- Digital channels might have different number of samples in same time (sample rate) as analog channels. Analog channels might have different sample rates based on what channels are enabled or what time base is.. These things change all the time. But all analog channels and digital channels will listen to same trigger engine (whatever you set it to trigger from) and all the channels will be correlated in time, so you can compare what happened when across the channels, analog or digital. And also since sampling more data at the same time, 8bit scope with only one analog channel enabled will need to process 6x less data per second than with 4 analog channel +16 digital channel. So enabling digital channels might slow things down, but not because digital channels are treated differently but because scope has much more data to process. That parameter will change from individual scope to scope model, even for the same manufacturer. |
| Someone:
--- Quote from: 2N3055 on April 18, 2023, 01:49:53 pm --- --- Quote from: Someone on April 18, 2023, 11:57:37 am --- --- Quote from: 2N3055 on April 17, 2023, 11:53:59 pm ---I don't know of any current production scope that has software triggers (out of mainstream brands i know off). I certainly don't know them all naturally. --- End quote --- --- Quote from: 2N3055 on April 18, 2023, 09:57:14 am --- Pico 3406D has less than 0.6 µs [blind time] --- End quote --- Arent Picoscopes in that category of software based serial triggers? At which point the best case blind time of captures is irrelevant when talking about sustained throughput. --- End quote --- There is no software triggers in Picoscope.. You have wrong information. Do better research before stating something as a fact.. --- End quote --- Really? where do they advertise hardware serial triggers? where are examples or documentation of that? Why do they not correct people on their own forums who say the serial triggers are software? |
| Someone:
--- Quote from: pdenisowski on April 18, 2023, 06:52:23 pm --- --- Quote from: 2N3055 on April 18, 2023, 06:27:45 pm ---Trigger event is start of capture event, it cannot happen again until scope fills the whole requested time period + rearm time... --- End quote --- Yes. People sometimes forget that the waveform update rate may also be limited by the user settings: if you have 100 ms/div and 10 divisions, the maximum waveform update rate for any oscilloscope is < 1 waveform per second -- it will take 1 full second just to perform a single acquisition :) --- End quote --- While datasheets like to publish the lowest achievable dead time (and highest update rates) they are always with the little * or acknowledgement that they are the best case. Often re-arm time changes with parameters like memory depth, or it has a minimum that can occur between some acquisitions but that is not guaranteed with occasional longer gaps. The re-arm time is rarely (never?) a constant. For many complex questions like these the only option is to test in the specific application, oscilloscopes being such complex and configurable devices that they cannot detail/explain every possible use case (or might not want to talk about their shortcomings). |
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