Problem with digital trigger pattern

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sarns
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Joined: Mon Jun 03, 2019 9:01 am

Problem with digital trigger pattern

Post by sarns » Mon Jun 03, 2019 9:13 am

Hello,

I set up a digital trigger pattern in PicoScope 6. I want to trigger when D0-D3 are all Low and when on D4 appears a falling edge. In 90% of the captured signals the system triggers on the right pattern, but sometimes it catches a signal like you can see on the screenshot where D3 is High instead of expected Low. I tested these setting with PicoScope 5xxx and a 2xxx. Both devices have the same results. I would appreciate help with hints what I'm doing wrong.
Attachments
trigger.png

Gerry
PICO STAFF
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Posts: 494
Joined: Mon Aug 11, 2014 11:14 am

Re: Problem with digital trigger pattern

Post by Gerry » Tue Jun 04, 2019 9:25 am

Hi sarns,

Could you post the psdata file as I need to see the actual trigger and data to be able to help you.

Regards,

Gerry
Gerry
Technical Specialist

sarns
Newbie
Posts: 0
Joined: Mon Jun 03, 2019 9:01 am

Re: Problem with digital trigger pattern

Post by sarns » Tue Jun 04, 2019 9:32 am

Hi Gerry,

see the attached file. Trigger was set like in the post above.
Attachments
20190604-0001.psdata
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Gerry
PICO STAFF
PICO STAFF
Posts: 494
Joined: Mon Aug 11, 2014 11:14 am

Re: Problem with digital trigger pattern

Post by Gerry » Wed Jun 05, 2019 11:42 am

Hi sarns,

Could you tell us exactly what your Digital probes are connected to (for instance, if it is the legs of a chip on a PCB, what is the output type and signal switching levels for the output pins of the chip). Could you also photograph your connection setup and post the image.

Then could you do the following:

Set up a Repeat Trigger and set the Maximum Waveforms to be captured to a value of 50 (Tools->Preferences->General->Waveform Buffer). Perform captures on one of the Scopes as before, using the same Trigger setup but put A&B analogue channel probes on the connection points used for D3 and D4 on the DUT (instead of digital probes) and select a 'Logic Trigger' using 'A' AND 'B' (with a threshold of 1.5V, and the default hysteresis) click 'Used', select the 'Logic' value of 'AND', then set the 'Digital' trigger pattern to just D0-D2 low, and finally click on 'Used'.
Then perform the captures and, when complete, flick through the captured waveforms using the waveform 'Buffer Overview' (the compass icon) and send us the psdata files where the trigger fired when the analogue channel being used for D3 was still high on at least one of the 50 waveforms (if there is one).

Next, could you go back to your original setup (using the digital channels of D3 and D4, and just the 'Digital' trigger), then click on the Digital Channels and groups, set the Logic Type to 'custom' for the lower bank of digital channels, and change the threshold to 1.2V. Then perform the captures as you were originally, to see if you still get the false triggering on D3.
Finally, could you set the Logic Type back to TTL, swap the connection points on the DUT over for D0 and D4, then perform the captures as you were originally, to see if you get the false triggering on D1.

Regards,

Gerry
Gerry
Technical Specialist

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