USB 6009 analog input - DIO Issue

[Path_Tech]

I recently laid out a printed circuit board to connect to the USB 6009.  There is a single ground plane layered in the board for both the digital and analog circuits on the board.  The digital IO is activating a relay (via port 1) while port 0 is broken down to three digital outputs(P0.0-P0.2) and one digital line (P0.3)  Furthermore, there is a 1-5 volt signal that I'm monitoring (I've tried RSE & Differential) on AI0.

The problem is that when I have my digital lines & ground hooked up to the board, I get a 0.8 volt reading on my analog input.  To further clarify, I have no power running to the circuit board when I get this reading but I get the same reading regardless.  If I disconnect the digital lines, the analog input reads 0 volts as it should.  I should also point out that the voltage that I'm trying to read from my circuit board is from the output of an op amp/buffer.

I've used the USB 6009 (or similar NI products) for many years now but this has me stumped.

[DollaBrillz]

Below, I have attached a link to USB 6009 user manual. On page 17 is the input conguration. I would suggest taking a look at the configuration and seeing how your set-up differs.

http://www.ni.com/pdf/manuals/371303m.pdf

I would be also be interested to find out the behavior when you run a task. When you start the task and run it, if you set the value to 0V, does it read 0V? Also, if you stop and then clear the task, does the value settle at 0.8V or 0V?

I hope this helps!