Rigol 1104Z+, confused by time base and serial decode

[linuxha]

Hi new to this forum so if this is in the wrong place please point me in the right direction and I'll post there.

I have a nice new Rigol 1104z+ that I'm still getting used to. I've used older (used) scopes with lots of buttons and dial but the menus of the Rigol still hold lots of secrets for me. I've been playing with the serial decode and I find that the results are greatly affected by the time base. I've clicked auto and it gets me a decode of a single ASCII character on the screen. If I change the time base so I can see more bits I start to get more ASCII. If I go further it changes to different values and I'm left to wonder if my sanity is intack (different data that wasn't what was shown before).

So am I doing something wrong?

[ebastler]

It's important to realize that this scope only uses the screen data for the decoding -- i.e. if you cannot clearly distinguish the individual bits visually on the screen, the decoder cannot distinguish them either. Also, if the data starts with an incomplete byte at the left edge of the screen, the decoder may struggle to get in sync.

Not all DSOs work this way; in fact the majority use the deeper and longer capture memory to feed the decoder. But Rigol implemented it this way on the DS1000Z series so get by with limited computing power. This can be a rather annoying limitation for decoding, but unfortunately there is no workaround I am aware of.

Edit: Well, you can't do anything about the limited time resolution. But you can make sure that the screen data starts with a complete byte (by adjusting horizontal position manually) to help the decoder get in sync right away.

On the bright side, I don't think you are doing anything wrong... 

[linuxha]

Thanks, very useful information. I'm wondering if I could save the data over the Ethernet and view it. Might help with validating the data. At the moment I don't have a spare port on the switch, 

[ebastler]

You can transfer the recorded trace data via SCPI commands, and I believe the decoder results as well. (See "event table" SCPI commands, ETABle:..) It's all documented in a separate Programming Guide which is avaliable as a free download. I have never used this myself however, so can't give practical advice here.

I'm afraid the SCPI approach does not work around the restriction of decoding from the screen memory only, hence you would not really gain much.

You could also use the Rigol just for data aquisition and do the decoding on the PC via sigrok. This would give you the ability to capture and analyse larger chunks of data than via the scope's built-in, one-screen-at-a-tim decoder. The scope's serial triggers can still be useful to start capturing at the relevant time.

Sigrok should support the DS1000Z series; I believe you can connect either via Ethernet or via USB (device port on the back of the scope). Again, no experience of my own here, but maybe others can chime in.

[Fungus]

Thanks, very useful information. I'm wondering if I could save the data over the Ethernet and view it. Might help with validating the data. At the moment I don't have a spare port on the switch, 

Yeah, but it's very slow and inconvenient.

Question: How "new" is it? Honestly I'd send it back if possible and get a Rigol DHO804 instead. The DS1054Z is an antique by comparison.

(sorry to be the bearer of bad news...)

[linuxha]

I'll try the Ethernet link to see the results. The good news is I don't need to resolve this immediately because the issue that triggered this is resolved (problem at a connector). I now see perfect ASCII at 9600 baud.

I wouldn't mind looking at a trace as long as it has enough info to figure out what happened. :-)

[Karel]

DSRemote can connect to DS1000Z series scopes via ethernet and can decode also UART.



https://www.teuniz.net/DSRemote/