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Does it matter how the RTSI cable connects between devices on the PCI bus
ATE_Dude_22
08-22-2013 01:05 PM
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I have 4 test systems that use 4 PCI devices (6602 Counter, 5421 ARB, 6225 DAQ, 5114 Digitizer), registered in MAX as Dev1, Dev2, etc....
3 of the 4 systems use the exact same base computer systems (i.e same tower, same motherboard, same processor, same amount of RAM, etc....), the 4th is a different style computer but the PCI card configuration is the same.
All 4 systems use the RTSI cable to connect all 4 PCI cards for timing, but the "**bleep**" system's card configuration is different in terms of which slot which card is installed in because of depth limitations with cabling to the motherboard.
My question is, can this difference in physical configuration have an effect on the overall system performance, or in other words, does it matter which device is connected to the next in the serial chain provided by the RTSI cable?
Tim-C
08-25-2013 10:36 PM
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The only thing you would need to worry about is signal propogation delay. The longer the signal travels on a ware, the longer it takes to get there.
National Instruments
Applications Engineer
John_P1
08-26-2013 10:55 AM - edited 08-26-2013 10:56 AM
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I mean... you're talking about a few hundred ps of propagation time with such short distances (1 foot per ns is a pretty good approximation of the speed of light). It really shouldn't matter--are you seeing any unusual behavior?
Best Regards,
08-26-2013 11:04 AM
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Well, I had an issue on the machine in question that was related to the device database in MAX. It showed 2 devides listed that were not even installed, nor could I delete them from the configuration?? I ended up downloading a tool from NI to repair the database, and that seemed to fix that issue.
As far as performance related to the card configuration with the RTSI cable, nothing that "jumps" out as a performance problem, I just haven't had a lot of experience with configurations that use the RTSI cable, and was just looking to see if the positioning in the RTSI chain can make a difference (outside of length of wire which I would assume the performance of the RTSI is certified, as we buy them as an assembly from NI)
