Serial(UART) Triggering Issue on SDS1104x-e Scope - Page 1
Forum section: electronics / beginners

author: Dundarave
author_rank: Regular Contributor
timestamp: December 02, 2018, 06:00:46 am
content: Checking with the Siglent scope experts: I'm new to DSOs, have recently acquired an SDS1104x-e, and I'm trying to capture the serial output going to my Picaxe board (i.e. the programming port) as an exercise to learn how to use the serial decode functionality.However, despite following the manual very closely, I cannot figure out how to get the scope to even trigger on the "serial" trigger setting with the UART protocol selected, let alone decoding it. If I set the trigger to "serial" and the protocol to I2C, it triggers on my serial signal just fine. But if I set the protocol back to "uart", the scope simply ignores my serial input.I've set the "9600, 8, N, and 1" parameters, set the Trig Bus for "idle level low" (that seems to be what's coming out of the comm port -> USB adapter), and re-checked every other setting (and have futzed around with them all as well in desperation).I can't find any info in the manual about the actual serial/uart triggering criteria, i.e. what parameters are crucial, etc., and thought I'd ask here if anyone has gone through similar frustration and has discovered the hard way some absolutely critical parameter in the serial/uart trigger setup that I've overlooked. I've also checked that the baud rate shown on my terminal software (termite), matches the baud rate of Windows Device Manager comm port driver (i.e. the Picaxe USB/serial cable driver), and lines up with the baud rate that set for the UART trigger.Any suggestions? Once I get it to trigger properly, then I can move on to actually trying to get the scope to decode...Thanks for any help!

author: tautech
author_rank: Super Contributor
timestamp: December 02, 2018, 06:55:32 am
content: Screenshots attached to a post help us diagnose what mistakes are being made.STB3 UART signal.Like many protocols they are Idle high so a falling edge trigger is best to use so to trigger on the very start of the byte instead of the first rising edge.Also, trigger holdoff can be lengthened so the trigger is not rearmed when part way through the byte, not doing so accounts for much unstable triggering when decoding.Here we have the holdoff adjusted to larger than any of the visible packets.So once the channel is assigned and thresholds set we set the various fields in the Configure menu.P2Note, all the above are done with ordinary trigger settings and no Decode trigger settings made with which you can set actual bits to trigger on. To get up and running it's a good idea to just get things working with standard triggers and the various Decode settings before diving into the Decode trigger settings however after obtaining stable triggering you can transfer your basic trigger settings into the Decode trigger suite with a single press of the Copy to Trigger button.A bit of playing around and you'll find the ways that suit your methodologies best.

author: Dundarave
author_rank: Regular Contributor
timestamp: December 03, 2018, 02:43:59 am
content: All good now, tautech! Thanks very much for the enlightening help.I was getting completely confused by the triggering setup arrangement, and it was your advice about "copying the trigger settings" using the "copy from" button in the decode menu that clued me in.I couldn't figure out why I was getting presented with the same trigger parameters in different screens, and they never seemed to work in decode mode. So I got the signal triggering reliably outside of the decode mode, using some holdoff time as suggested, then transferred the whole trigger setting enchilada over to the decode suite with a push of the magic button (sothat'swhat that's for!), and the decode started working instantly.Thanks again: that's one new area of scope functionality down, probably 50 or so to go... Good thing I've got plenty of time, lol. (I've recently retired and I'm finally getting back to my electrical engineering roots after a busy career in internet software development & management).