SDS-1104X-E, trigger holdoff feature (it may say test) - Page 1
Forum section: electronics / testgear

author: CiscERsang
author_rank: Regular Contributor
timestamp: December 15, 2019, 11:24:55 am
content: Hello guys again,I've decided to make a separate topic on this matter.A need has arisen on watching how many times a frame is being sent per second. The point is, I'm not sending that frame with a frequency ~10000 times per second. Physically impossible stuff with my HW.I've used trigger settings withholdofffeature in order to get only one trigger event per frame appearance (this way I understand howholdofffunctions).And what I have:Firstly I found out the frame length (ms) by means of coursors. Then I set trigger with holdoff feature.A question: to me it looks oddly enough that holdoff enable/disable doesn't affect (f=) frequency in any way.Perhaps I'm doing something wrong.first pic is where holdoff is enabledsecond pic is where holdoff is disabled (as I undestand it's disabled judging on button's state. Or?)thanks in advance!P.S. of course I've re-triggered that many times. There's no difference in terms of frequency changing.

author: 2N3055
author_rank: Super Contributor
timestamp: December 15, 2019, 01:25:12 pm
content: Quote from: CiscERsang on December 15, 2019, 11:24:55 amWhy this topic? Performa01 already answered.Holdoff works fine. It's frequency measurement that confuses you.That frequency measurement you see on the screen is frequency of signal on the screen, not frequency of trigger events.So it is based on baud rate of packet, not on how many packets you send per second.In order to get frequency of trigger events, you need to measure frequency of Trig output on the scope.So connect any device that can measure frequency (multimeter, second scope, frequency counter ) to trigger out and measure.You might even be able to to do it by looping back Trigger Out to one of input channels on your own scope and try to measure frequency of THAT channel.

author: CiscERsang
author_rank: Regular Contributor
timestamp: December 15, 2019, 01:57:13 pm
content: Quote from: 2N3055 on December 15, 2019, 01:25:12 pmYou know, I read your detailed answer. After that I had returned to Performa01's answer and reread his answer one more time. Now, I understand what he meant.Both answers complement each other or so.However, still can't get how to check if holdoff is working.

author: 2N3055
author_rank: Super Contributor
timestamp: December 15, 2019, 02:15:50 pm
content: Quote from: CiscERsang on December 15, 2019, 01:57:13 pmIt is working, don't worry.If you set timebase to so your data packet is longer than screen, you might get unstable trigger without holdoff, because it will trigger on the beginning of packet and again on somewhere on the rest of the packet. With trigger holdoff it will insert delay, so it will stabilise...

author: CiscERsang
author_rank: Regular Contributor
timestamp: December 15, 2019, 02:32:57 pm
content: Quote from: 2N3055 on December 15, 2019, 02:15:50 pmyes, sometimes the frame skipped left. Now it had stopped doing that.

author: Performa01
author_rank: Super Contributor
timestamp: December 15, 2019, 02:50:36 pm
content: Holdoff is working fine, but it's difficult to demonstrate its function in situations where it's not required.Holdoff just disables the trigger for the set amount of time - and it won't affect the trigger frequency counter (which just tells an average frequency of the gated input signal on the trigger channel).Holdoff is normally not set to the burst (packet) length, but slightly less than the time interval of the gap between packets and is intended to get a stable trigger on the first trigger condition within a packet. Unstable triggering usually happens when packets with multiple valid trigger conditions are arriving at a high repetition rate and there is not much space in between them.If for example you have a packet every 4ms and your packet is 2.42ms long, then you could set the Holdoff just below the timespan of the gap between packets, which would be 4 - 2.42ms = 1.58ms. In this example, 1.57ms Holdoff should work to get a stable trigger.Btw, seeing the packet rate is easiest done taking advantage of the deep memory. Just increase the timebase until you capture two packets instead of just one. You can then use cursors to measure the time period from packet to packet. If you need it very accurate, you can use zoom to fine-position the cursors.If the repetition rate of the packets is very low, so that you need to increase the timebase to several seconds per division, you might need to engage peak detect acquisition mode in order to capture the pulses of the packet reliably. In that case, precision of the cursor measurement will be low correspondingly, but for slow actions like this great accuracy is usually not required and you don't need Holdoff in such situations for sure.

author: tautech
author_rank: Super Contributor
timestamp: December 15, 2019, 07:29:12 pm
content: Quote from: CiscERsang on December 15, 2019, 11:24:55 amYou are.Some examples.Half of a CAN pair for clarity.First, Holdoff = Close (IIRC 70ns)Because the trigger gets rearmed, stable triggering is not possible as there are several edges within the packet that will be triggered on.Setting Holdoff to large amounts of time is made simple with use of the virtual keyboard that is accessed by pressing the multifunction knob when Holdoff is selected. This virtual keyboard is available in the same way for many types of adjustments in X and X-E scopes.Simply we make a setting longer than the longest packet to ensure the trigger is not rearmed until after the packet is finished. By using Run/Stop we can freeze the display and use the graticules to measure the packet length and decide on a suitable Holdoff time.Trig Out frequency will then be representative of the Holdoff settingandthe waveform characteristics.If we need to determine the Baud rate we can use Cursors set to the Start's of subsequent packets like the quick example below.

author: CiscERsang
author_rank: Regular Contributor
timestamp: December 16, 2019, 06:26:02 am
content: Quote from: Performa01 on December 15, 2019, 02:50:36 pmThat's it! But withoutholdofffeature I couldn't get any following packets on the screen. Now it's stabilized and I can, and of course now I can measure gap between them.Quote from: tautech on December 30, 1974, 01:56:55 pmhello tautech! How are you? Hope fine.to find out baud rate roughly I do that different way. As a variant.measure duration of a single burst by means of cursor option (for example I've got ~52us)then 1000000/52 = 19230, this value corresponds 19200 baud standard.

author: 2N3055
author_rank: Super Contributor
timestamp: December 16, 2019, 08:16:18 am
content: Quote from: CiscERsang on December 16, 2019, 06:26:02 amBaud rate will simply be 1/t of shortest pulses in a packet.

author: tautech
author_rank: Super Contributor
timestamp: December 16, 2019, 08:18:23 am
content: Quote from: CiscERsang on December 16, 2019, 06:26:02 amPretty good, and you ?Pleased with the Professor's selection ?

author: CiscERsang
author_rank: Regular Contributor
timestamp: December 16, 2019, 05:09:38 pm
content: Quote from: tautech on December 16, 2019, 08:18:23 amSure, I am.This gear is running ten hours a day since purchasing. it's my eyes when I'm struggling with buses.Not pleased with buses and other cr*ppy hardware.