CRIO-WR clock export


#1

Hello all,

I haven’t been able to find any info on the ability to export the clock from the CRIO-WR or the time with other NI modules. Could anyone please tell me whether this is possible?

Greetings,

Alonsy


#2

Hi @Alonsy,

I’m no expert in CompactRIO, perhaps someone else can give you a better answer.

As far as I can see, from both the schematic (page 12), as well as the HDL (line 176), there is no dedicated clock and/or time interface output on the backplane.

There’s essentially an SPI interface and a few unused digital I/O pins.

Now, if you follow the SPI signals inside the HDL, you will see that they end up in a little module called cmp_crio_arb, and they are used to access the WR time. In particular they provide access to the link_ok and time_valid flags, as well as to the TAI time.

Having said that, keep in mind that access over SPI is slow. By the time you’ve retrieved the current WR time, it will be way past.

Cheers,
Dimitris


#3

Hello @dlamprid ,

Thanks for your reply.
I have been trying to find out how other cRIO modules share their clocks(which protocol etc). My search has been unsuccessful, it seems this data is behind a NI paywall.

But I think it is not SPI and I think SPI communication is not fit for what I require.

Kind regards,

Alonsy