Author Topic: Can the Rigol DS1054Z decode/trigger on TTL RS232?  (Read 590 times)

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Offline sofakng

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Can the Rigol DS1054Z decode/trigger on TTL RS232?
« on: February 06, 2019, 12:38:42 pm »
I'm new to oscilloscopes and I'm trying to learn using my Rigol DS1054Z.

Can it trigger and decode TTL (3.3v) RS232?  I've tried enabling RS232 trigger and decode but neither one seemed to be working properly.  It would sometimes trigger OK, but then the decode was completely incorrect.
 

Offline orion242

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Re: Can the Rigol DS1054Z decode/trigger on TTL RS232?
« Reply #1 on: February 06, 2019, 01:16:58 pm »
Shouldn't have a problem with it.  Was using it for 232 decode right before I replaced it with the 5074.

Make sure all your settings are correct, trigger level and polarity.  Also if bytes fall partially off the display it can get all hosed up.  Its really decoding just what's displayed on screen.  Keep that in mind when scrolling in time.
 

Offline sofakng

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Re: Can the Rigol DS1054Z decode/trigger on TTL RS232?
« Reply #2 on: February 07, 2019, 01:59:10 am »
OK - Thanks.  Is it correct that TTL has "positive polarity" (3.3/5v = 1, 0v = 0).  Is this different than RS232 (+12v = 0, -12v = 1) ?

Also, should I need to change the Analog Channel Threshold Setting?  (Math -> Decode -> Auto Thre.)

Thanks again!
 

Offline Doctorandus_P

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Re: Can the Rigol DS1054Z decode/trigger on TTL RS232?
« Reply #3 on: February 07, 2019, 03:17:36 am »
I find a Logic Analyser a much better tool for examining (TTL-level) RS232 signals.
I usually use my oscilloscope only to verify there are no shorts and the logic levels are decent.

Then I use Sigrok with cheap (USD 5) hardware from Ali.
https://www.aliexpress.com/wholesale?SearchText=24MHz+8ch
A PC monitor with mouse is a pretty good interface for a Logic Analyser.
With Sigrok / Pulseview you also get many more serial signal decoders than your oscilloscope would have:
https://sigrok.org/wiki/Protocol_decoders
> Number of currently supported protocol decoders: 98.
 

Online newbrain

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Re: Can the Rigol DS1054Z decode/trigger on TTL RS232?
« Reply #4 on: February 07, 2019, 04:01:39 am »
OK - Thanks.  Is it correct that TTL has "positive polarity" (3.3/5v = 1, 0v = 0).  Is this different than RS232 (+12v = 0, -12v = 1) ?
Yes, and yes.

Also, should I need to change the Analog Channel Threshold Setting?  (Math -> Decode -> Auto Thre.)
You can try to set it at about half Vcc.
I have no problems in decoding TTL serial (understanding the known limitation that orion242 pointed out), but in general use a falling edge trigger. If signal integrity is really bad there might issues triggering.
Nandemo wa shiranai wa yo, shitteru koto dake.
 

Offline orion242

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Re: Can the Rigol DS1054Z decode/trigger on TTL RS232?
« Reply #5 on: February 07, 2019, 01:05:25 pm »
Also, should I need to change the Analog Channel Threshold Setting?  (Math -> Decode -> Auto Thre.)

That's how you set it up for standard 232 levels, TTL or etc.  You should be able to auto / normal trigger, catch a signal, then its pretty clear to match the icon of positive/negative polarity in the decode menu.  Its pretty straight forward.  Note there are thresholds for both TX/RX off memory.
« Last Edit: February 07, 2019, 01:08:24 pm by orion242 »
 

Offline David Hess

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Re: Can the Rigol DS1054Z decode/trigger on TTL RS232?
« Reply #6 on: February 07, 2019, 02:54:55 pm »
OK - Thanks.  Is it correct that TTL has "positive polarity" (3.3/5v = 1, 0v = 0).  Is this different than RS232 (+12v = 0, -12v = 1) ?

All RS-232 level translators are inverting so CMOS/TTL signal levels from UARTs have the opposite polarity.  External CMOS/TTL RS-232 "compliant" interfaces break this standard of course because why not, Garmin?
 

Offline sofakng

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Re: Can the Rigol DS1054Z decode/trigger on TTL RS232?
« Reply #7 on: February 08, 2019, 01:25:26 am »
Thanks so much for the help everybody!

I'll try some additional tests and see if I can get it working.
 


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