NI PXI-7813R frequency

[KKAU]

Hi,

Can i use PXI-7813R module to genarate and measure ferquency arround 15MHz. What is the maximum frequency i can generate and measure using NI PXI-7813R module.

Thanks in Advance.

Krishna

[MarcoMauri]

HI!

NI PXI-7813R has got 160 digital lines configurable as inputs, outputs, counters, or custom logic at rates up to 40 MHz.

If what you want is to generate a sinewave @ 15MHz, If I'm not mistaken, you should consider another product.

Marco

[KKAU]

Thanks Marco,

I need to generate and measure square wave only. I tried with  sample VI, FPGA PWM in 1ch Simple with Generator.vi and Host PWM in ch1 Simple with Generator.vi   got from http://www.ni.com/example/26494/en/ . But able to generate and measure up to 2.5MHz only. is there  way to change this VI to work up to 15Mhz.

Krishna

[crossrulz]

Well, let's look at this.  Each wait is at least 2 clock cycles.  The writing of the output is a clock cycle each.  And you could likely throw another clock cycle or two in there for the loop maintainance.  So right there is at least 6 clock cycles.  That puts you at 6.7MHz.  And since you are writing directly to those controls from the host, that is a few more clock cycles for the communication.  16 clock cycles (2.5MHz) for all of that is not a stretch by any means.  I'm not really seeing any way to tweak some bandwidth out of this.  Sorry, but you need a faster FPGA or a dedicated counter that can do this.

[T-REX$]

I'm gonna (sorta) disagree... I don't think you should call it quits yet. That said, your current programming approach won't get you there. For higher performance, you're going to have to use Single Cycle Timed loops. You won't be able to use the Wait for Rising Edge node anymore, but a simple Feedback Node + Greater Than will accomplish the same thing. You'll also have to ditch the waits and Tick Counts. You can implement your own counters via shift registers and an increment function. for the waits, you'll just have to "do nothing" for X cycles. A State Machine architecture should let you do that pretty easily.

It'll take time to implement for sure, but I'd argue that it's feasible to get 15MHz performance out of this target from the programming side. The only thing that I'm worried about for your app is the DIO isn't made to go that fast. I believe most of our R-Series boards have the DIO rated to a max of 10MHz due to HW limitations. For anything faster, you'd need a FlexRIO + HSDIO FAM. Otherwise you're risking signal integrity. If you really need to switch at 15MHz, you need a board with IO rates designed for that. If you just need the logic to perform faster (ie. not switching every 15MHz, just being able to respond that fast) then I think you'll be fine.

EDIT: Forgot about this doc: http://digital.ni.com/public.nsf/allkb/59798CF4FF6F7F12862574B4005BE70C

Check out the sample waveforms, and see if a specific rate is good enough for your app.