Using external clock source with R series FPGA cards

[tintin_99]

Hi,

I need ns resolution for some setup hold time measurements using 7813R or 7820R FPGA cards.

Is it possible to use exterbal clock source for my timed loops  with frequency of 1GHz to get 1ns resolution

Thanks

[Artem.SPb]

You plans run this timed loop on FPGA part or on your PC?

[tintin_99]

I plan to run the timed loop in target side ( FPGA ) and I should eb able to sweep a delay in nS reseloution . 

[Artem.SPb]

No, you can get only 25ns.
But what you plan to do with this speed? DIO can work on 40MHz. but this speed is guarantee, you no need external control

[Intaris]

---

@Artem.SPb wrote:

No, you can get only 25ns.
But what you plan to do with this speed? DIO can work on 40MHz. but this speed is guarantee, you no need external control

---

Where do you get this 25ns from (I found out - see below)?  Speed is not everything, synchronisation is sometimes king. Hence driving NI hardware AND external equipment from a single timing source is desireable.

We use a much older card and we have external clocks and code running in loops up to 160MHz.  That's a lot less than 25ns per loop. And we use external clocks.

Having said that, 1GHz seems rather fast, I don't know if your card supports that.

Edit: Specifications for the 7820R say that is supports external clocks up to 80MHz only, and while that's faster than the 25ns Artem mentions, it's still a long way from 1ns.

It also seems like the 7813R is an even older card than we are using, which really only supports up to 40MHz (now I see where Artem gets his 40MHz from - links would be very valuable).  If you would read the specifications of the cards, your question would have been very easy to find.

[dan_u]

You don't need to synchronize to a 1 GHz clock to have 1 ns resolution. A derived clock would do. If you have a precise 10 MHz or 40 MHz clock you can derive clocks from these, but definitely not up to 1 GHz. It will be difficult to compile any loop on the Virtex-II target (7813R) above 200 MHz, giving you a 5 ns resolution. I think the maximum clock for a Virtex-II is 210 MHz. For the Kintex-7 you can probably reach around 400 MHz, but I doubt 1 GHz is possible.

There's no official way to synchronize a Virtex-II card to an external clock afaik. For the Kintex-7 this is possible (up to 80 MHz).