What is the RTSI device count limit?

[CCI_Test]

I am in a little bit of a bind, and I hope one of you guys/gals can help me out.  Another engineer at our company spec'd a system that contains 7 PCI based cards (6552 HS-DIO cards) and he didn't realize that NI only sells RTSI cables up to 5 positions.  

My question is this:  is there a physical limit of 5 boards on a cable, or is it as this thread suggests, 8?

http://forums.ni.com/ni/board/message?board.id=250&message.id=1052

Reason I ask is I put a 7 position cable together (although only two were hooked up) and the Synchronize call into TClk was throwing errors.  As soon as I replaced the cable with a 2 position one, the errors went away.  I suppose it's possible that it's a poorly constructed cable, but I'd be happier to hear that it'll work once I hook 7 devices up.

Thanks!

-Mike

[Jesse_O]

Mike,

There is no hard limit in software limiting TCLK to 5 boards.  When you TCLK devices together, one of the devices will export a 10MHz clock and this is a possible limitation.  This clock is routed to every board, and with increased cable length and increased devices numbers on the cable you can degrade the signal quality.  Having poor signal quality between boards can cause TCLK failures. 

In your case, you only have 2 devices on your cable and you are getting errors.  This suggests that the cable you are using is the problem.  Perhaps we can provide more information based on the error you are getting.  Also, there are a couple tests you can perform to see if anything helps.  If you change the position the RTSI cable is connected (cards in connector 1 and 2 to connector 1 and 7) are you able to run your code, or does the error change?  Are you able to try another brand of cable?

On a side note, PXI is designed to support synchronization of a large number of cards.  NI sells chassis with 18 slots, and with a timing and synchronization board multiple chassis can be synchronized together.  This is the easiest way to tclk large numbers of boards together.  If you are wanting to use a chassis with a PC, MXI can be used instead of a dedicated controller.