Capture RS485 burst on Rigol ds1052 - Page 1
Forum section: electronics / beginners

author: Wartex
author_rank: Frequent Contributor
timestamp: August 03, 2011, 10:22:45 pm
content: Oscilloscope noob here. How do I capture a 2 second burst of RS485 traffic at 4800 bps on a Rigol scope? What do I press? "Silence" signal has 100 mV noise.

author: vk6zgo
author_rank: Super Contributor
timestamp: August 04, 2011, 01:24:45 am
content: At my last job,we tried to do this with an analog storage Oscilloscope,with the same problem of high level noise on the line in the "silence" period.We really only wanted to see if the signal was there & not mangled in any way.RS485 as we used it, was as a 2 wire system with neither wire at earth potential.We ended up cheating,as the line went into a Max485,so we just looked at the signal after conversion to PIC compatible levels.Have you tried using both channels in the quasi-differential connection?Most people on this forum sneer at it,due to poor common mode rejection,but it does work OK in many cases.We didn't try it because we had the opportunity to "cheat".The fault we were chasing turned out to be internal,& nothing to do with the data link!VK6ZGO

author: IanB
author_rank: Super Contributor
timestamp: August 04, 2011, 02:49:17 am
content: Doesn't RS485 use a differential pair for signalling, with +ve and -ve halves of the signal on each wire?Mike recently did a video on RS485 on YouTube where he displayed scope traces. It seems we need Mike to drop in and say how he configured his scope for those measurements.What I think Mike did is display each half of the differential pair on a different channel relative to the common signal ground. Can you do that?

author: Psi
author_rank: Super Contributor
timestamp: August 04, 2011, 06:11:06 am
content: The rigol isn't very good at doing pseudo differential using both channels but it works well enough to have a general look at the signal. Last time i tried it on the rigol there was quite a bit of noise compared to my old analog scope in pseudo differential mode. You wouldn't want to be looking at a really low level signals with it

author: Wartex
author_rank: Frequent Contributor
timestamp: August 04, 2011, 11:46:08 am
content: Thanks for your responses, but no one has answered the question: How do I RECORD the waveform? What do I need to press on the scope to make it capture?

author: bilko
author_rank: Frequent Contributor
timestamp: August 04, 2011, 11:47:38 am
content: Set triggering to single shot mode to capture waveform, go into trigger menu and select 'sweep single'

author: MikeK
author_rank: Super Contributor
timestamp: August 20, 2011, 09:58:41 pm
content: This prompts a related question of my own. When you capture the signal to a file it only captures a screen's worth. Is there any way to get the entire signal? I had to piece together 5 screens, which was tedious.

author: Mechatrommer
author_rank: Super Contributor
timestamp: August 21, 2011, 12:38:30 am
content: Quote from: MikeK on August 20, 2011, 09:58:41 pmGoltek Capturecan do that in a breeze,help file here. but with 2 seconds capture duration as OP requested? that can be a problem, i never tested for that duration.

author: MikeK
author_rank: Super Contributor
timestamp: August 21, 2011, 02:54:48 am
content: Brilliant!