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A newbie needs some help with my first DSO
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vk6zgo:
In the early days of DSOs, memory depth was of much greater instant impact on everyday use of a 'scope to look at complex analog signals.
One standard use was to look at one, or several analog video fields, to look at aberrations on the blanking level & sync part of the waveforms.

To this end, to accommodate the around 40ms duration of two fields, the 'scope would be set to around 5ms/div.
Early DSOs often quoted quite decent sample rates, but these were only valid for much faster time/div settings.

At these slow timebase rates, the memory would soon run out of capacity, so as the sweep time was increased, the sample rate was reduced, until a complex wideband video signal became totally unrecognisable.

Over time, memory depth slowly, then rapidly, increased, until that original problem has pretty much disappeared with decent affordable DSOs, & the other niceties of memory depth have become the primary topics of discussion.

There are still DSOs available which are sufficiently low in memory depth that the old problem raises its head. They are usually very cheap, or old.

Electro Fan:

--- Quote from: 2N3055 on May 31, 2024, 10:37:03 am ---Today when you say "logic analysers and protocol analysers" people think you mean Saleae type USB device.
Which basically have no triggering to speak of, only very rudimentary one.

--- End quote ---

2N3055, please elaborate on why this is and why LA makers don’t include more/better triggering?
(Clearly digital only LA’s can’t trigger on analog signals but once a signal is in a digital realm specifying trigger conditions should not be too hard - yes?). Thx
2N3055:

--- Quote from: Electro Fan on June 01, 2024, 12:38:59 pm ---
--- Quote from: 2N3055 on May 31, 2024, 10:37:03 am ---Today when you say "logic analysers and protocol analysers" people think you mean Saleae type USB device.
Which basically have no triggering to speak of, only very rudimentary one.

--- End quote ---

2N3055, please elaborate on why this is and why LA makers don’t include more/better triggering?
(Clearly digital only LA’s can’t trigger on analog signals but once a signal is in a digital realm specifying trigger conditions should not be too hard - yes?). Thx

--- End quote ---

I'm afraid I don't know why they don't.
I would presume it is because many of those USB protocol decoders (like Saleae) are simple USB streaming devices that have no logic on primary hardware side, but simply stream data to software.
There are some USB LA/PA that have some logic, and have various degree of triggering, but you need to search for them.
But even those don't have very sophisticated triggering that old LA used to have.
nctnico:
With more memory, triggering becomes less important. Especially on a logic analyser which has a capture -analysis workflow. I have a high-end logic analyser from Tektronix with a programmable trigger statemachine which can trigger on sequential and logical conditions beyond your wildest dreams. But it is extremely rare that I use that feature. My logic analyser has so much memory and a time stamped mode that it can collect extremely long time spans. In many cases I don't care about a trigger condition, I just hit the 'run' button to make a single acquisition. That single acquisition has all the information I need. The search & analysis features of the software help me to find problem areas and correlate cause & effect. Then again, I fire my logic analyser up when my MSO runs out of steam but that is unlikely to happen. I find myself using an MSO for 99% of the measurements I used to use a logic analyser for.

My first logic analyser only had like 1kpts or 2kpts of memory. Triggering on very specific conditions was very important as the memory was short. Getting a full picture of cause & effect typically required taking at least several measurements, storing / retrieving data and comparing. It did the job but getting a result (as in identify a problem) could take very long.
tggzzz:

--- Quote from: nctnico on June 01, 2024, 03:14:39 pm ---With more memory, triggering becomes less important. Especially on a logic analyser which has a capture -analysis workflow. I have a high-end logic analyser from Tektronix with a programmable trigger statemachine which can trigger on sequential and logical conditions beyond your wildest dreams. But it is extremely rare that I use that feature. My logic analyser has so much memory and a time stamped mode that it can collect extremely long time spans. In many cases I don't care about a trigger condition, I just hit the 'run' button to make a single acquisition. That single acquisition has all the information I need. The search & analysis features of the software help me to find problem areas and correlate cause & effect. Then again, I fire my logic analyser up when my MSO runs out of steam but that is unlikely to happen. I find myself using an MSO for 99% of the measurements I used to use a logic analyser for.

My first logic analyser only had like 1kpts or 2kpts of memory. Triggering on very specific conditions was very important as the memory was short. Getting a full picture of cause & effect typically required taking at least several measurements, storing / retrieving data and comparing. It did the job but getting a result (as in identify a problem) could take very long.

--- End quote ---

The key point about complex triggers and filters is that they reduce the amount of "noise" in the captured data. Reduced "noise" reduces the importance of long capture buffers. While I will, reluctantly, eyeball 1kSamples of data, there's no way I'm going to trawl through 10MSamples of data!

I'll discuss this in "logic analyser terms"; the equivalents with protocol analysers shouldn't be difficult to work out :)

The simplest kind of filter is "clock rising edge", since that removes crap that is irrelevant to your state machine implementation. If you have a 1kHz state machine clock and sample at 10MS/s, that immediately removes 99.9% of the "data".

The next kind of filter is to only look at information to/from one device on a bus. Sometimes the filter can be as simple as a single CE line, sometimes it involves recognising an address.

Closely allied to that is only capturing information in (filtering) or after (arming/triggering) your FSM has entered a specific state.

In many cases you want to be able to demonstrate that something has not occurred. In such cases the capture depth is, of course, irrelevant; you just let the analyser rip and hope/expect to see it still waiting when you return after your coffee break. That kind of analysis is difficult without
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