Logic Triggering Using A Threshold and A Level

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dfergenson
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Logic Triggering Using A Threshold and A Level

Post by dfergenson »

I implemented a system to add a holdoff feature to my PicoScope 5444A. Basically, I want to lock triggering out for about eight milliseconds after a trigger in block acquisition mode but when I ran into trouble I reverted to the PicoScope app to debug it. I am using the latest version on both Mac and Windows (6.14.44.5870) and my scope has Driver version 2.1.61.2597 and Firmware version 1.3.3.0/1.1.5.0.

My main goal is to trigger off of a negative edge on Channel A (-30 mV) and I'm able to do that. Upon triggering, I have the built-in function generator send a TTL pulse to trigger external hardware that moves a line low for 8 milliseconds after the trigger event is received. After that, that line reverts high. I route that input into the scope at Channel D.

To achieve what I want seems pretty straightforward at that point. I should trigger off of a logical condition of:
Channel A, Level, -0.030V, direction falling
AND
Channel D, Level, 1V, direction above.

I did so and the system would not trigger. When I removed the Channel D requirement, triggering resumed and I could see that the Channel D input was clearly operating as intended. Triggering worked with all logical combinations other than AND and NAND. I tried changing Channel D's trigger conditions to a window with appropriate window boundaries and that also did not help.

Am I missing something obvious? Or does a 5444A not support logical triggering off of a level or something? Or is this unexpected behavior?

I've included photos here in case someone can use them to help point me towards something that I am doing wrong.
Screen Shot 2021-06-14 at 12.05.43 PM.png
Screen Shot 2021-06-14 at 12.05.55 PM.png

Gerry
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Re: Logic Triggering Using A Threshold and A Level

Post by Gerry »

Hi dfergenson,

When you deactivated the trigger on Channel D, Channel A is firing and capturing D going low which is the start of the hold-off period. So A and D triggers are not being seen in your capture, even when you deactivate D, because the D trigger is 8ms away (i.e. the rising edge that you don't see).

To be able to use logical AND triggers, the triggers need to both be within the capture period.

What you could do instead is send the Channel A Trigger also to a simple circuit to just condition the Trigger signal (i.e. set the level, and use a Schmitt Trigger to provide some hysteresis for any noise, after buffering it if it is also a signal you need to measure) and use the conditioned signal for your external hardware Hold-off.

Regards,

Gerry
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dfergenson
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Re: Logic Triggering Using A Threshold and A Level

Post by dfergenson »

Thanks, Gerry.

If I understand your response, because Channel A's falling edge AND Channel D's high level were not true at the same time, I was unable to trigger off of the condition of Channel A experiencing a falling edge while Channel D was high.

And that was absolutely the condition in the photographs. But this was because I deactivated Channel D's test condition from the logical triggering in order to exhibit the behavior of the electronics where Channel D was sent low. If I had included Channel D's level test, then Channel D would have been high until a Channel A falling edge was detected and at that point a trigger should have occurred.

But the scope did not trigger on Channel A AND Channel B under this circumstance. The giveaway that something was amiss was when I switched the trigger condition from Channel A AND Channel B to Channel A NAND Channel B. Certainly if Channel A AND Channel B failed to trigger then, by definition, Channel A NAND Channel B should have triggered.

If I'm confused on any of these details, I would definitely like to know it, especially if my triggering scheme would not be expected to work.

Thanks for your support.

-David

Gerry
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Re: Logic Triggering Using A Threshold and A Level

Post by Gerry »

Hi dfergenson,

Okay, it's a bit to hit and miss to try and decipher what is going on from images. Could you post data files of the conditions that you setup, and explain what you were expecting to happen from each one.

Regards,

Gerry
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dfergenson
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Re: Logic Triggering Using A Threshold and A Level

Post by dfergenson »

Gerry,

I certainly understand that it can be difficult to infer what I was trying to do from those screenshots.

I've attached a setup file to this post and also a diagram.

In the diagram, you can see that the PS5444A has two inputs active, A and D, and that its signal generator is also active.
LockoutTraceDiagram.001.png
The trigger is set for a condition where A hits a negative going edge when D is logic high. Upon triggering, the signal generator produces a square wave which starts a lockout timer. The lockout timer's enable out is connected to D in and is brought low for 9 milliseconds, preventing triggering from occurring during that time. When the lockout time has elapsed, the lockout timer's enable out line is brought high again and the scope will then trigger on the next event on Channel A.

I've verified the proper functioning of the lockout timer but I can't get the triggering to occur on A falling edge AND D above level.

I can communicate with you directly via phone or video conference if it would help to further clarify things and I appreciate your time either way.

-David
Attachments
TriggerExample.pssettings
(3.75 KiB) Downloaded 150 times

bennog
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Re: Logic Triggering Using A Threshold and A Level

Post by bennog »

Can it be the D signal is already low when the A signal gets the negative edge ?

can you post a .psdata file with only trigger on negative edge of A.

Benno

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Re: Logic Triggering Using A Threshold and A Level

Post by dfergenson »

5444DError.png
Thanks, Bennog.

As you can see from the screen shots in the initial post, the D signal was definitely high when the triggering occurred off of the edge on A.

Things are slightly more complicated than I thought but I've been able to trap the error (or something a lot like it) for reproduction.

The problems that I was having were on my 5444A. That is at a field site with a customer and I've returned to my own laboratory now where I have a 5444D. The 5444D does not have the same problem but it does have a similar one when using OR or XOR.

I've attached a .psettings and a data file as well as a screen shot to this post.

On my 5444D, I have no problem triggering off of Edge A AND Level D. But I cannot trigger off of Edge A OR Level D. And, of course, if Edge A OR Level D is always false then Edge A NOR Level D must always be true but that does not trigger either. This mirrors my problems with my 5444A using the AND and NAND logic triggers.

To reproduce my conditions:
Connect Gen to Channel D.
Set the horizontal resolution at 1 ms/division.
Set the vertical resolution at +/-50 mV for Channel A.
Set the vertical resolution at +/- 5V for channel D.
Set the signal generator to generate a square wave at 100 Hz with an amplitude of 2V, an offset of 0 Volts, Sweep Mode inactive, Trigger Mode active, Trigger Source Scope, 1 cycle per trigger.
Set complex triggering with logic. Set triggering on channel A to be a level, falling below 1 mV and no hysteresis. We want to trigger A off fo noise. Set triggering on channel D to be a level, below 1 V and no hysteresis. Make sure to check the "Used" box on both the Channel A and Channel D trigger tabs.
Use AND logic initially to make it work on a 5444D (or not work on a 5444A). Use OR logic for it not to work on a 5444D (or to work on a 5444A).
NAND does the same thing as AND. NOR does the same thing as OR.

It's possible that the differences between my 5444A and 5444D experiences are based on some other thing that I'm doing wrong differently in two places but I'm pretty confident that I've trapped an error of some sort.
Attachments
PS5444DError.pssettings
(3.67 KiB) Downloaded 164 times
PS5444DError.psdata
(1.74 MiB) Downloaded 160 times

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