Can the Rigol DS1054Z decode/trigger on TTL RS232? - Page 1
Forum section: electronics / testgear

author: sofakng
author_rank: Regular Contributor
timestamp: February 06, 2019, 01:38:42 am
content: 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.

author: orion242
author_rank: Unknown
timestamp: February 06, 2019, 02:16:58 am
content: 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.

author: sofakng
author_rank: Regular Contributor
timestamp: February 06, 2019, 02:59:10 pm
content: 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!

author: Doctorandus_P
author_rank: Super Contributor
timestamp: February 06, 2019, 04:17:36 pm
content: 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+8chA 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.

author: newbrain
author_rank: Super Contributor
timestamp: February 06, 2019, 05:01:39 pm
content: Quote from: sofakng on February 06, 2019, 02:59:10 pmYes, and yes.Quote from: sofakng on February 06, 2019, 02:59:10 pmYou 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.

author: orion242
author_rank: Unknown
timestamp: February 07, 2019, 02:05:25 am
content: Quote from: sofakng on February 06, 2019, 02:59:10 pmThat'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.

author: David Hess
author_rank: Super Contributor
timestamp: February 07, 2019, 03:54:55 am
content: Quote from: sofakng on February 06, 2019, 02:59:10 pmAll 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?

author: sofakng
author_rank: Regular Contributor
timestamp: February 07, 2019, 02:25:26 pm
content: Thanks so much for the help everybody!I'll try some additional tests and see if I can get it working.