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How does waveform updates on an oscilloscope work? Why do they work that way?
radiolistener:
--- Quote from: ballsystemlord on April 17, 2023, 04:41:16 am ---Doesn't this cause a problem for protocol analysis?
--- End quote ---
No, protocol analysis is done at full speed on FPGA logic with no dead zone.
Regarding to waveform capture, it works in that way because it requires some time for processing before show it on the screen. It requires some time for processing.
Actually it doesn't matters, because signal is captured by trigger which works on FPGA logic at full speed with no dead zone. Dead zone happens between trigger events, more fast CPU and FPGA allows to minimize dead zone.
Also, note that usual analog oscilloscope also has dead zone, when the ray is out of the display or in back trace state. It needs some time to return ray back on the left side, and analog oscilloscope don't display signal at this time.
radiolistener:
--- Quote from: 2N3055 on April 17, 2023, 12:35:35 pm ---I really don't understand software and hardware TRIGGERS mentioning ...
--- End quote ---
some cheap Chinese toys don't have FPGA to implement hardware trigger which works at full ADC speed in real-time, they just capture some long sample and then using software trigger. In that case important signal event can appears in dead zone and such software "oscilloscope" may lose such signal event in a dead zone.
2N3055:
--- Quote from: Someone on April 18, 2023, 11:57:37 am ---
--- Quote from: 2N3055 on April 18, 2023, 09:57:14 am ---First I am talking about decoding and looking at serial protocol data on scope ( that is what OP asked about). Not about general scope use.
--- End quote ---
1500 words on and you still try to talk about what you want to talk about. Ignoring the OPs question, and taking a long long time to add in the honest details..... :=\
--- 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.
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--- 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.
Yes you want to talk at length about non realtime serial analysis/search. But dont make out like that is some replacement for all realtime cases, or add mountains of half-truths and misleading drivel.
OP asked really clearly what is the interaction between dead time/update rate and serial decode, that has been covered quite well in a non biased and polite manner.
--- End quote ---
There is no software triggers in Picoscope..
You have wrong information. Do better research before stating something as a fact..
I've grown tired of being called dishonest by you..
Everything I said is true and founded in facts. On equipment I have and use and have verified...
Very unlike speculations and generalizations...
I answered to OP. Adding to data that was biased and wrong, stating that hardware decoding has influence on scope retrigger time.
It does not. It has influence on screen refresh of decoded strings but no influence on triggering.
At least on software decoding scopes I have here. So if there are scopes out there that do have that problem it is NOT because they software decode, but because they have BAD IMPLEMENTATION of software decoding...
Pdenisowsky gave some good info..
Where he said that MXO4 is fast because decoding is in hardware and that it can easily capture packets that are 10µs apart.
News flash, if they are only 10µs apart that is a piece of cake for 3 software decoding scopes I have here...
ballsystemlord:
--- Quote from: Someone on April 18, 2023, 11:57:37 am ---
--- Quote from: 2N3055 on April 18, 2023, 09:57:14 am ---First I am talking about decoding and looking at serial protocol data on scope ( that is what OP asked about). Not about general scope use.
--- End quote ---
1500 words on and you still try to talk about what you want to talk about. Ignoring the OPs question, and taking a long long time to add in the honest details..... :=\
--- End quote ---
If the OP, me, might interject for a moment.
Not knowing how oscilloscopes do their protocol decoding, I asked how dead time affects triggering. The question, with respect to the analog part, has been answered in that it was pointed out that all, or almost all, scopes use HW based decode-triggers. Or so I understand from your posts.
Just to be clear, decoding is necessary for triggering because a 1 and a 0 look like any other 1 and 0 until you decode what the bus is trying to transmit.
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 $$$ and buy a scope that could do protocol analysis, and it can, via the web interface. So, does the scope have blind time with it's digital channels so that I can't trigger on them at certain points during the capture? IDK. I'd ask rigol, but every question I've ever asked them has gone unanswered. I've tired email and phone without result. The phone just goes to a voice mail.
2N3055:
--- Quote from: ballsystemlord on April 18, 2023, 04:41:40 pm ---
--- Quote from: Someone on April 18, 2023, 11:57:37 am ---
--- Quote from: 2N3055 on April 18, 2023, 09:57:14 am ---First I am talking about decoding and looking at serial protocol data on scope ( that is what OP asked about). Not about general scope use.
--- End quote ---
1500 words on and you still try to talk about what you want to talk about. Ignoring the OPs question, and taking a long long time to add in the honest details..... :=\
--- End quote ---
If the OP, me, might interject for a moment.
Not knowing how oscilloscopes do their protocol decoding, I asked how dead time affects triggering. The question, with respect to the analog part, has been answered in that it was pointed out that all, or almost all, scopes use HW based decode-triggers. Or so I understand from your posts.
Just to be clear, decoding is necessary for triggering because a 1 and a 0 look like any other 1 and 0 until you decode what the bus is trying to transmit.
It was also said,
--- Quote from: JPortici --- The moment the analog signal is correct you should switch to a protocol analyzer (which can usually also put data on the bus, which makes it a much more useful trigger. Imagine doing CANbus analysis of a network with only an oscilloscope).
--- End quote ---
Which brings us to the most advanced part of the question, which I didn't think I'd ask. Now my own scope has 16 digital channels (MSO5074 LA). I was trying to save myself a few $$$ 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 ---
No, scope decoding is separate from serial triggering. Triggering has it's own "decoder" that is used for triggering. It is a state machine that gets set by scope for trigger. After trigger scope captures certain time length (decided by timebase or manual memory setting) and then gives such captured data to analysis engine for full decode of all captured data.
On Siglent scope you can easily disable on screen decoding but use serial trigger... They are separate.
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...
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