Not related to previous "slope trig fail" things.
Many times I have seen peoples wonder what data trigger engine get when system use low sample rates.
Earlier, I presented some superficial conceptual picture of the principal structure of a system with respect to where the trigger engine is in the system. It is after ADC. It do not use decimated sample rate.
Next two images show one example how it affect in practice. This working mode we can name as SARI. Sequential Acquisitions Random Interleaving. Siglent do not tell anything about it.
Example in next image signal 1st harmonic (base) is 1.8 times over fNyquist and it have least over 5 times fNyquist frequency components what are high level. Of course this example is done for demonstrate what happen there so usually no one use just these settings for just this signal. Also there is CH2 open for nothing... except for drop ADC real samplerate to 500M. Also memory is set small for rise decimation to 10:1 just for better demonstrate this SARI.
Signal is 45MHz "square" but its true risetime is also nearly what can see. As can see scope display sample rate 50MSa/s.First image, gif animation, have 16 TFT frames repeating. It looks nearly as scope looks in real but real world it looks bit better.
Display mode is dots. SARI mode need dots mode.
Persistence is turned of for also better imagine situation so that really can see it continuously trig and trig position is right.
Every TFT frame include, least mostly, 16 acquisitions overlaid. Every single acquisition have 7 samples.
Every single acquisition sample interval is constant 20ns naturally but these 7 sample groups are in random time time position.
1st image is this continuously running situation as much as in real word with this setup. Oscilloscope true frame interval is continuous and roughly 40ms.
2nd image. It is one single frame from this 1st image animation.
If you count dots it can see there is 16 sequential acquisition. I have marked one individual acquisition with red circles.
Now if you think The Trigger Engine. Look one red marked acquisition. It do not look like at all this signal. But it is right positioned. Trig'd, and well.
It need know that even if we have just only one single shot what is this red marked trace (7 dots) it is Trig'd.
But as can see these dots do not meet trigger at all. So, it have trig'd but display do not show reason!!
It is still part of our signal and well match with it... if we get more these well trig'd group of sequential samples we can see they are perfectly trig'd and positioned and show our signal. If you take just one shot it trig but then you look image... no reason, is it false trig... no. It is not.
We are working lot of over fNyquist. And our scope trig. But now carefully. This is not ETS!
This mode can show signal image if signal is enough continuous just also as in ETS mode. But this SARI works ONLY with decimated samplerates!!! It still can be good to know and use in some special situations. Of course this do not work at all if you turn interpolation on. Sinc or linear. It just can not. Naturally.
It also demonstrate in practice this fact that Trigger engine in this scope get really other than decimated sample rate.
Look, think carefully, do not loose thinking logic. Keep fun.
SARI mode. Scope do not have ETS but it have SARI what works something like ETS with decimated sample rates. True frame interval is roughly 40ms "
Sidenote. In this example with this setup wfm/s is very low around 400. Theoretical maximum is over 7000 with this setup with "ideal scope" but of course it do not exist in real world in this time layer.
One single frame from upper animation.
One single acquisition marked red in this single frame.
Can you see this red marked one acquisition displayed data that it have something why it is trig'd.
(I repeat, this have nothing to with fail slope trig discussed at same time in this thread, this is just only for demonstrate what it also mean when Trigger engine get true ADC data instead of decimated data.)
Look it, think carefully, do not loose thinking logic. And Keep Fun.
Note, this not "Siglent only". Of course same kind of things are in many modern scopes with digital trigger engine. Not perhaps same but something like this. How it perform - some better - some worse.