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sampling a digital bus

maaz2020

Hi,

I've created a digital bus from an analog bus b<4:0> from VIVA Measurements -> Anaog to Digital menu. I would like to sample this bus at regular intervals, I've tried the sample and the value functions from calculator but none of them work

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  • You seem to have removed the pictures of your expressions, but as far as I know, the value function works now (this was fixed in IC6.1.7 ISR15 from what I can tell from a quick search; it certainly worked for me in the latest IC6.1.8 hotfix version)

    I don't believe sample is supported with buses. A workaround would be to convert the bus back into a analog voltage (could be between 0 and 32) using Measurements->Digital to Analog (and choosing to convert the entire bus) and then sample that instead. This worked when I tried it.

    Andrew.

  • in reply to Andrew Beckett

    Thanks for your reply, it seems to work actually (may have done something wrong along the way). I still have some weird results though:

    my analog bus is in A

    in B I have clipped it to some useful interval

    in C I have created the digital bus, from Measurements -> Digital to Analog, and also have plotted  the bus sampled at (t0 + T)  and (t1 + T), where t1 is one period after t0 and T is the period, 1ns

    in D I wanted to plot the difference of those two samples buses but I get odd results in volts (should expect the difference of the two decimals):

    this is the formula (the hidden bit is the model files definition)

  • in reply to maaz2020

    OK, what's happening is that if you subtract two digital buses (or two digital signals) there's an automatic conversion to analog, assuming 5V full-scale. Since this is a 5-bit bus, you'd get 5V for code 31. The difference here is 6, and so you're getting 5.0*6/31 = 0.9677419 (i.e. what you're seeing). 

    What you might want to do is rather than relying on this automatic conversion with the default values of 5V, you might instead want to use the digital to analog measurement to convert it to 31V full-scale, and then subtract those. The results will still be in volts, but at least the numbers would match the numbers on the bus.

    It would be nice of course if you could subtract one bus from another and get a bus output - but that's not available right now...

    Andrew.

  • in reply to Andrew Beckett

    Yes it does make sense to convert back to analog for post-processing.

    Thank you very much for your help.

    M

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