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Gw Instek GDS2204E (200MHz 4 channel DSO) review
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CC555:
with less memory the scope decodes at lower sample rates:



but if 10 Mpts is selected:

At 10 MS/s it doesn't decode the signal (clk = 100 khz):


It needs 20 MS/s, that is a 0.5M buffer  :-\:


I don't know if my settings are 100% right but I would say this oscilloscope has a problem decoding serial buses with the memory and sample rates selected.


--- Quote from: rhb on December 24, 2017, 04:00:28 pm ---*&#@!!!

I bought an MSO-2204EA precisely for this task!

--- End quote ---

Me too, uCs and serial buses.



nctnico:
I think the firmware engineers at GW Instek cut a corner by skipping (too many) samples when decoding deep memory. This should be easy to fix for them though at the expense of speed.
rhb:
My SWAG is that it is a consequence of Object Oriented Programming.  Instead of decoding a short buffer and logging data to a long buffer it's trying to decode the entire buffer whatever the size.

I may be wildly wrong as I've not looked into the matter yet.  All I know is what's been posted here.  But I've seen similar effects from OOPS, for example drawing 6 curve traces by drawing 1, erasing it and drawing 2, erasing them and drawing 3, etc.  Looks damn stupid if you're drawing 6-10 curves.  Intelligent users tend to giggle a lot looking at that.

The decoder should be operating on a small window as data comes in.  That window should slide along the buffer as samples come in.  The observed behavior suggests that it is always starting the decoding at the start of the buffer.

This is a clear argument for open source scope application code.
tautech:

--- Quote from: CC555 on December 24, 2017, 05:58:23 pm ---I don't know if my settings are 100% right but I would say this oscilloscope has a problem decoding serial buses with the memory and sample rates selected.

--- End quote ---
What would concern me more is the displayed signal integrity ? Not so much the scopes ability to portray it but the glitches and the variances in the data idle voltage of ~1/2/div.  :-//

Something's maybe not right with your digital circuit or probing technique.

Jump back out of Decode and see what waveform shapes and amplitude you get then.

CC555:
Hello tautech,

I think there is not any problem with these glitches, they are real and always show up when clock is low during a communication so It is the slave who is controlling the data line and can generate them.




And I have to check if the decodification is in the right place in the pictures. Anyway I am going to use a saleae logic to decode the bus.

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