I have 2 test stations that use the PCI 6533 DIO, I had a a requirement to build another test station and had to go with the PXIe 6536. I am in the process of updating all my VI's that use Traditional DAQ drivers to DAQmx. I have come across a problem that has beaten me up. The code works on the PCI6533 cards. I have taken a Logic analyzer and captured a plot of the good DIO. When I am using the PXIe 6536 would appear to be loaded down or nonexistent when testing a UUT. When no UUT present and I test just the DIO it seems to be there. My question is what has changed between the 2 types of DIO's that would load down a signal like this. There has got to be some line or something that is loading it all down.
Any help would be appreciated!!!
What is the input impendance of your UUT? Digging through the PXIe-6536, I found a 50 Ohm output impedance spec. I couldn't find anything similar for the PCI-6533. So the impedance mismatch is likely your problem.
"The output impedance of the NI-6533 will be approximately 15 to 40 Ohms (<20 ohms typical) and the input impedance is 100 kOhms."
Here's the data sheet for the 6535-7 family, for your reference: http://sine.ni.com/ds/app/doc/p/id/ds-114/lang/en
Note that the output impedence spec is 50Ω, but input impedence is "High-impedance" (50 kΩ to ground). It's hard to give you much more information without knowing your application though.