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DPO7354 decoding SPI signals

DPO70000SX, DPO/MSO70000, DPO7000 Series, DPO/MSO5000 Series
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Joined: September 11th, 2019, 5:44 am
Country: Belgium

DPO7354 decoding SPI signals

Post by mvdeplas » September 11th, 2019, 6:05 am

Hi, I'm using the DPO7354 and everyone now and then I need to find a specific event in a larger SPI event, and every time I do this I run into the same issue with this scope.

So I set the Trigger to Advanced and configure the source signals to what is needed (SS, MOSI, SCLK) and set the threshold levels to about 50% of the swing.

I want to view a specific write instruction (1 0000 1100 0000 000x) so I set it to trigger on MOSI and set the correct serial pattern in the editor. But, no matter what I do I can't make the scope trigger on this sequence.

A work-around is to shorten the serial value to 8 bits. Then, the scope triggers but because this shorter value is not unique within the larger data set, I get several unwanted triggers instead and I can't analyze what I need.

When I trigger on the 8-bit value and I get lucky, the scope triggers on the correct even. So I know there is an occurrence of this pattern in the event, but it seems like the scope cannot trigger on anything larger than an 8-bit word.

I was wondering if this is more common (I don't see this is a known limitation of the scope), or if there is something I'm missing...
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