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Siglent 1202X-E Serial Decoding not working

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mwb1100:

--- Quote from: Hexley on October 31, 2023, 12:01:22 am ---An experiment to try: change the Arduino to send 2 stop bits and see if the scope can decode "AA" then. Or, insert a program delay before sending the second "A", and see how that affects the error.

--- End quote ---

Beat me to the punch!  I had a long reply queued up to suggest configuring the arduino for 2 stop bits to see if that made decode work.

The second photo in the first post shows that the 10 bits used to send the first 'A' character takes 1.040ms including start & stop bits.  So the arduino has the correct timing.  If having the arduino send 2 stop bits fixes the SDS1202X-E's decode, then that's an indication that there's a problem in the SDS1202X-E decoder that Siglent will likely need to fix (or at least weigh in on a workaround).

mwb1100:
Also, I'm testing with an SDS1104X-E and don't see the problem unless I deliberately misconfigure the decoder.  I didn't realize it, but the 2 channel SDS1000X-E and the 4 channel SDS1000X-E scopes have very different firmware histories (it makes sense that they'd have different firmware builds, but I expected their releases would closely follow each other in both changes and release timing).

The 2 channel firmware history only mentions one UART decoder related fix: "Fixed the bug of UART decoder with some special settings"

The 4 channel firmware history mentions that fix and 3 others (none of those other 3 seem like they'd be related to this problem).

Mag748:
Good observation! The decode does work when a large enough delay is added between bytes. And I did configure the serial port to use 2 stop bits, and decode works as well.

The settings for stop bits does make a difference to the envelope. It’s as if the stop bits setting is internally being doubled or something.

The photos attached are with the arduino sending 2 stop bits and different decode stop bit settings applied.

mwb1100:
Seems like you will need Siglent's help.  I wonder if the problem got introduced by the "Fixed the bug of UART decoder with some special settings" in firmware 1.3.27?

I don't know if Siglent lets you easily downgrade firmware.  If so it might be worth trying 1.3.26 to see if the problem goes away.

As for your question about

--- Quote from: Mag748 on October 30, 2023, 12:45:03 am ---As a side note, can anyone recommend a decent, and good value for the money logic analyzer capable of UART decode?

--- End quote ---

You can get good results with a $10 Saleae Logic clone and the sigrok software - I haven't actually used one of these, but from all the reviews and tutorials out there it's clear that they work.  An example review/tutorials on youtube is this (cued up to where he starts talking about UART decoding):

  - https://youtu.be/7x4h7Zq2NNU?t=730

One thing about the cheap logic analyzers - they generally can't handle the voltage levels of RS232 signals (which are often +/-5V or more in magnitude).  UART levels are fine (0 to 3.3V or 5V).  If you need the RS232 levels supported, you'll need to move up to something a bit more expensive (but can still be less than $100) such as a Kingst or DreamsourceLab DSLogic logic analyzer.  Or run the RS232 through a level shifter.

I have a DSLogic U2Basic 100Msps with 8MB hardware buffer RAM on board (a knockoff, I'm sure, from eBay) and it works well with UART decoding.  They seem to run around $60-80 on eBay right now.

Mag748:
See attached response from Siglent. It would seem they feel it’s functioning as designed. Interesting…

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