7I70 as a logic analyzer

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02 Jan 2021 01:28 #193781 by faeluke
How fast can I run a 7i70 as a logic analyzer to better understand how my machine works before I tear it apart?

If I limit the number of channels, can I get a faster sampling rate?

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02 Jan 2021 01:35 #193783 by tommylight
Replied by tommylight on topic 7I70 as a logic analyzer
Roughly 500 reads per second, if i remember correctly, but i think setting the servo period to 500000 would make that 1000.
Theoretically that should be 1000 and 2000, but i will leave that for PCW to confirm as he is the Grand Master of Mesa boards.
As for the LinuxCNC scope, it can do much more as it can be set to use a base period that is much faster than the servo period, but far from the real scopes.
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02 Jan 2021 01:38 #193784 by PCW
Replied by PCW on topic 7I70 as a logic analyzer
The sample rate will be the servo thread rate (typically 1 KHz)
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02 Jan 2021 15:39 #193846 by faeluke
Replied by faeluke on topic 7I70 as a logic analyzer
PCW,
Given that this is not running a CNC, how fast can I run the servo thread if my "logic analyzer" is the only operation that I care about? My current setup is a 7I92, a 7I74, and a 7I70.

I run less than 50uS of latency with my current setup. Do you think it would pull in data at 10KHz?

Thanks in advance!

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02 Jan 2021 16:22 #193850 by PCW
Replied by PCW on topic 7I70 as a logic analyzer
3-4 KHz is probably about as fast as a Ethernet connected device can run (with the right host hardware)
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02 Jan 2021 17:25 #193858 by Mike_Eitel
Replied by Mike_Eitel on topic 7I70 as a logic analyzer
@pcw
Out of curiousity.
What is the rise ( slew ) time of your inputs?
Mike

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02 Jan 2021 20:26 #193886 by PCW
Replied by PCW on topic 7I70 as a logic analyzer
The 7I70 (and 7I66,7I76, 7I84 etc) field input time constant is about 50 usec
the inputs are oversampled by an A-D at between 60 and 150 KHz per input

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02 Jan 2021 21:50 #193894 by Mike_Eitel
Replied by Mike_Eitel on topic 7I70 as a logic analyzer
Thx
And habe a good 2021

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