Learning triggering tecniques on Siglent 1104 - Page 1
Forum section: electronics / testgear

author: tony359
author_rank: Frequent Contributor
timestamp: June 24, 2020, 08:52:24 pm
content: Hello all,I've upgraded my old analogue Fluke scope with a shiny Siglent, 1104X-E. So far, I love it, the potential is incredible.I wanted to ask the community for some help with triggering signals as I would like to improve on this subject to better use my scope.I have two scenarios I'd like to show you.1. Digital signal, this is a serial signal from a 8-bit shift register of an Apple //e machine which will eventually be translated into video. Check the video below, the trigger seems to "lose it" every second or so. I resolved by adding a bit of hold off but I am not sure I understand why? The signal should be basically stationary as the video was static when I took the video2. Composite PAL. I had issue triggering the PAL output of the aforementioned Apple //e so I connected a PS3 - I know the Apple//e uses some non-standard ways to generate colours. Please see below: Why am I unable to get a clean signal picture there? There is some other signal overlapping on top.Would anybody be able to help me?Thanks a alot!Tony

author: tautech
author_rank: Super Contributor
timestamp: June 24, 2020, 09:17:25 pm
content: 1. Holdoff is set to Close when it should be set to packet width + which is ~4ms to prevent retriggering within the packet.When you select Holdoff and press the multipurpose control a virtual keyboard becomes available to make selection of large holdoff values easier.Stable triggering on aseries of eventslike clock bursts or data packets is much easier using a holdoff setting just a little wider than the total time of the event.

author: tv84
author_rank: Super Contributor
timestamp: June 24, 2020, 09:32:39 pm
content: 2 things:One of the best ways to see "random" problems in a PAL signal can also be with a TV.If, as you say, the image doesn't seem to show nothing (on TV), it can be a signal (for example, Macrovision protection) that occurs on the Vertical Sync (not visible on screen, usually...).You seem to be triggering on the Hor. Sync.Change to triggering on Vert Sync and do a accumulation of the signal in the Vert Sync areas (on both image fields) - the 6 or 7 lines following the VS.PS: I don't know the specifics of Siglent video trigger (but I would hope it to allow specify HS, VS or a specific line).

author: tony359
author_rank: Frequent Contributor
timestamp: June 24, 2020, 10:02:42 pm
content: Thank you for your help.Regarding the triggering of a series of event, I think I now understand the purpose of hold off. You're basically telling the scope NOT to try and trigger DURING the event as it WILL find some signal to trigger. I also now understand why it's stable for a second or so - the trigger event falls in the empty space - and the scope will end up triggering on the first event during this time. Thanks!Video signal: besides curiosity to see how it works, I was trying to assess why my monitor wouldn't lock on this composite signal in a stable matter. But let's say this is for educational purpose, I appreciate what you say about plugging the signal into a monitor!I did not see Vertical/Horizontal triggering option but I can indeed trigger on a specific line. I didn't know the first 8 lines were Vertical Sync, thanks. That explains the mess I see on screen even though I would expect a way to just show the video signal without the sync.Anyways, I am not sure I can do accumulation either - or if I can, I don't know how to do that. Please see the video below, I could see some specific lines - which could be enough if the signal wasn't still unstable for some reasons.

author: tv84
author_rank: Super Contributor
timestamp: June 24, 2020, 10:13:51 pm
content: Quote from: tony359 on June 24, 2020, 10:02:42 pmTony, that's not an unstable signal. That is a normal video signal!If that was unstable you would loose sync and the scope didn't show that. Only the video line came to black level in a few lines but that has to do with the image that you're seeing and nothing with a unstable signal.For what you are thinking as "stable" you need to get yourself a stopped frame. (for example: in a tvbox, dvd player, recorder or menu).

author: tony359
author_rank: Frequent Contributor
timestamp: June 24, 2020, 10:44:44 pm
content: TV84I see what you mean - but this is the PS3 welcome screen with the animation running, I do not think it has any black on it. I may be incorrect but to me it feels that the scope is incorrectly triggering on a black line when you see those flashes. If memory serves it doesn't matter what line I select, I get that "black flashing" on the scope.Please feel free to correct me and thank you a lot for your patience!

author: tautech
author_rank: Super Contributor
timestamp: June 24, 2020, 10:47:18 pm
content: Quote from: tony359 on June 24, 2020, 10:02:42 pmAll that exactly.Quite simple concept when you understand it and gives the user great power over how a scope displays signals of interest.There are a good few more features in these X-E's and we see you're already using a time offset to trigger on the left of the display. You can set that in stone so the horizontal trigger point remains static regardless of timebase setting.IIRC it's in the Utility menu.

author: tv84
author_rank: Super Contributor
timestamp: June 25, 2020, 08:08:29 am
content: Tony,Sure it has black.What I marked is a zone with mostly black content. Remember you're syncing on line 163. So, in the middle of the screen you should see black content (it may be fast but it has to be there...).I advise you to study a bit of video signals to learn how to interpret the levels you are seeing.As I said: stop the image of a video source and look at it in the scope. You won't see your "instability".

author: tony359
author_rank: Frequent Contributor
timestamp: June 25, 2020, 09:22:48 pm
content: Hey TV84Thank you. I thought that a better approach would require a white test pattern so I loaded one on the PS3 and played it. This way we know how the signal should look.What puzzles me is that sometime I get a stable signal, sometimes I don't. Also, depending on the time base the signal gets more stable or not.Below are a couple of examples. I believe it confirms that what we were observing before is a different line and not black on the signal.I understand what you are saying about stopping the scan - however the purpose of this is to learn things and also to make sure the scope works as intended as it's brand newI am not sure what's the "video" trigger is there for if sync lines are also overlaid on top, making the reading not very clear. Just by coincidence, today I was tuning a circuit where I had to watch a live PAL signal on the scope - there is where I cannot just stop at look at it.Again, just learning and I appreciate your help.Thanks for your help!

author: tv84
author_rank: Super Contributor
timestamp: June 25, 2020, 09:55:48 pm
content: Tony,Last try:Sure, those are white video lines. What you see sporadically is the transmission of black lines (so we can assume a black image). BUT they are totally well constructed. Stop calling it an "unstable signal"!If you had an unstable video signal the scope would be loosing sync all over!From what I see you have a correct signal an the scope is behaving correctly.If you don't like the black lines that you see appearing... talk to your video source.Do the following experiment: place a normal trigger between black and white levels. And try to see the frequency of those black lines events.That is a good exercise to practice with video signal analysis.

author: tony359
author_rank: Frequent Contributor
timestamp: June 25, 2020, 11:18:46 pm
content: I shall do.But why would I expect black lines on a white test pattern? Which are not visible when I zoom out...Unstable is definitely the wrong word. What I mean is that I feel that the scope is not showing me line 63 but a mixture of two.

author: vk6zgo
author_rank: Super Contributor
timestamp: June 26, 2020, 04:11:23 am
content: I wrote a lot of stuff, but lost it when I went looking for some pix to illustrate what I was saying, but I found these sites which do a better job!http://martin.hinner.info/vga/pal.htmlThis gives a lot of information in a fairly short description, but unfortunately, Martin uses an early generation DSO for the "field rate" picture.It is, at least, usable, unlike the horrors on the Wiki page.In any case, the line drawings make up for it.The other one shows practical displays photographed off analog waveform monitors or analog 'scopes.https://tv-handbook.com/Basic%20Video.htmlIn the first pix, incorrectly labelled "Two Horizontal Fields" (it should be "Horizontal lines"), if you look closely, you will notice that there is a visible "underline" along the blanking level.This is because a normal Oscilloscope or waveform monitor (WFM) display shows all the lines, including those during the vertical blanking interval, superimposed upon each other.This normally doesn't matter, but in the case of a 'scope with poor blanking, (or, as in the case of this pix, with the intensity wound up for better photos), the equalising pulses during the field group will become visible.As they only occur during that time, they are not normally anywhere as "bright" as the line sync pulses.Most waveform monitors, & some analog 'scopes, can display individual lines.WFM often have this capability, either with preset switch positions, or using a so-called "strobe" function, & ordinary analog 'scopes can do the same if they have a "delayed timebase" facility.I suggest you drag out your analog Oscilloscope & use it to examine the video waveform.The display should look pretty much like the ones in the second link, above.If so, you have a triggering issue with your DSO-----if not, there is a problem with your video source.PSI'm not familiar with your Oscilloscope, (or really any modern DSO), but if those two white arrowheads on either side of the screen are your triggering level, move them down to about mid amplitude on the sync pulses.Also make your triggering "negative going".

author: tautech
author_rank: Super Contributor
timestamp: June 26, 2020, 05:42:22 am
content: Quote from: vk6zgo on June 26, 2020, 04:11:23 amLH is channel 0V vertical position, RH is trigger level.Each are colored to represent the channel they are associated with.

author: tony359
author_rank: Frequent Contributor
timestamp: June 26, 2020, 11:23:05 pm
content: Hey @vk6zgoI know the feeling when you type a long post and then something happens and you lose it! Thanks, I appreciate the time you spent on this.Those links are very useful indeed. I have gone through them and I will do that again to make sure I fully understand the subject.I went to do some more tests as you recommended, I wired up my old Fluke analogue scope and the PAL signal from the PS3 (white field) was pretty stable, I couldn't see the same behaviour I previously observed on the DSO. Then I realised that being an analogue scope - which won't let me see a single line of signal - I would probably be unable to see a momentary black field as the CRT persistence would "hide" it.So I went back to the DSO and... there was no sign of the black line that we though came from the source. I tried different inputs and different probes but no, this time I could have a full white signal with none of those "flashing" which we thought represented a black line.Then I realised that if I enable some measurements - such as Peak to Peak - and I select some specific black lines towards the bottom of the screen, then the trace on screen starts jumping as there was some white as well - but the trace turns to constant Video black when those measurements are disabled.So I am a bit confused. All I think I can say is that what we were observing before was... some kind of anomaly as the scope now does not show any 'black video' when tracing a line in the middle of a white pattern.I can maybe assume some connection issues - I'm using some crocodile clips to intercept the signal going to the LCD. Still, they were happening pretty regularly - hence TV84 suggesting to check the frequency of the event - and I wouldn't expect some connection issues to generate a very regular and repetitive pattern on screen.What is your thoughts on this?

author: vk6zgo
author_rank: Super Contributor
timestamp: June 27, 2020, 01:58:05 am
content: Quote from: tony359 on June 26, 2020, 11:23:05 pmNope!It won't be a momentary "black field", as by definition, a "field" is a single scan of the raster from top to bottom.The beam completes a line, then moves downward, & does the next one, & so on, until it has done 312.5 lines--- it then displaces vertically slightly & does the same thing to complete the whole 625 lines of the interlaced display----a "frame", consisting of two fields.A momentary "black field" would still be synched correctly, so what you would see would, if you looked at two fields of the video waveform,as was customary, would be a "white field"followed or preceded by an occasional "black" field.Just such a signal was used in TV Transmitter testing.At horizontal rate, it would not be all that obvious, as it would simply appear as an "underline" to the existing white signal.Analogue 'scopes do not have very long persistence, their CRTs are very different to TV set ones, which are optimised for that.(If they did, they would not be useful for their intended function)As I said previously, Waveform monitors, & more "up market" analogue Oscilloscopes could, quite happily, look at individual lines.( you could even build up a circuit to allow a cheaper 'scope to do this).In any case, if you are looking at a particular line, your display should not change, unless you happen to be viewing a line which is part of a field which is changing, as is normal, if you are looking anywhere outside the vertical blanking interval, & watching live video.QuoteI really do think it was some kind of "finger trouble", due to unfamiliarity with the DSO.TV lines are about 64 us long, so in the greater scheme of things are quite "slow", so the 'scope should have no problem dealing with them.Fields are 10ms long, so should be even easier.The video information is "another kettle of fish", with components out to 5MHz.Older DSOs had major aliasing problems with this, as their sampling rates at field rate dropped so far that they couldn't resolve video information, resulting in an unusable display.Some were even reaching their limits at horizontal rate.Analogue 'scopes & modern DSOs have no problems with this.

author: tony359
author_rank: Frequent Contributor
timestamp: June 28, 2020, 10:00:12 am
content: QuoteProbably. Still, I shouldn't see a change in the signal when a measurement is added to the screen!But happy days. Thank you for your help and for all the links!