Digital Discovery Sync Mode Limitations

[RyanSullivan]

Hi there,

My company is developing a new testing system which involves using a logic analyser to capture signals being sent to a thermal printing mechanism. That data is then used to render a digital representation of a printout for validation purposes. We were previously using a Saleae Logic 8 for this purpose but we've recently purchased a Digital Discovery as we believe it may provide more flexibility in the sort of tests we can run.

The thermal printing mechanism has 6 signals. Two of those signals (clock and data) necessitate a sample frequency of at least 20MHz. The other 4 signals are much lower frequency. As captures can last an indefinite period of time and a high frequency is required, and since the Digital Discovery doesn't support compression, we've found that we need to use sync mode in order to not overflow the Digital Discovery's sample buffer. We currently have sync mode set to capture on both edges of the clock signal and the 4 lower frequency signals. We also have it set to capture on the most significant bit of a counter signal we generate from DIO 24-31 and feed into Din 8-15. This lets us calculate a timestamp for each sample.

With this setup the system mostly works. However we've discovered that the rendered printouts sometimes have a few missing pixels as you can see in this image:

I've had a look through the raw data and it looks like edges on the clock signal occasionally get missed. You can see here there are 2 repeated samples, between which I believe there was a missed rising edge on the clock signal:

I'm wondering if this is due to a limitation of sync mode? I noticed that in waveforms you can only set up to 4 triggers, whereas we have 6 set. Any help would be greatly appreciated.

Thanks in advance.

Ryan

[attila]

Hi @RyanSullivan

In Sync mode it can capture at most one sample every 10ns (w 100MHz).
At position 24754 probably the Motor2 signal falling edge was right before the Clock rise, so only the sample having Motor2-0 and Clock-0 was stored and Clock rising edge lost.

Can't you use normal capture mode (Repeated or Record) ?

[RyanSullivan]

Hi @attila

I see, thanks for getting back to me so quickly.

We tried using Record mode initially. It worked well for short captures but for longer captures we found that we couldn't transfer data off of the device fast enough to prevent the sample buffer overflowing. It would be ideal if the Digital Discovery could be set up to filter out samples that don't represent edges. However, from what I've read, I don't believe it has that feature. Are there any plans to implement something like that in the future?