I have a few questions about the situation you are experiencing with your dual PCI-6509 boards.
1. You mentioned that you are controlling TTL outputs with a DAQmx task. What are these outputs connected to? Are you driving anything with either of the boards?
2. More specifically, what is pin 34 connected to? Have you attempted to monitor pin 34 on the board assigned as the first device? When the pin floats to 1.3V, does it stay constant at this value or does it fluctuate?
3. What are the system specifications of the computer that you are running these boards in? Have you attempted to run both boards in another computer?
4. Is this a relatively new problem or has this setup ever worked? If it worked in the past, have there been any changes?
Let me know as much detail as you can and I will be happy to assist you further.
This is a duplicate post. Please refer to the following post for my response. Thanks!
Here are the answers to your questions:
1. It is one LabWindows/CVS windows task that creates 3 DAQmx tasks. The 3 tasks are 2 on Dev1, one controls DO for ports 0,10, and 11 to some switches, the other task controls DO for ports 1-9 that are connected to some vector modulators for signal generation. The single task on Dev2, the one that is having the problem, controls DO for ports 1-9 to some vector modulators.
2. Pin 34 is port 3.7 and is connected to a vector modulator. I have looked at the pin on Dev1 and see no problem. After the voltage floats to 1.3V, it seems to stay there.
3. The computer is an HP DX5150 MT running Win XP Pro with Service Pack 2. It is an AMD Athlon 64 Processor 3500+ running at 2.19 Ghz. It has 960 MB RAM. The NI software is the following:
CVI Run-Time 220.127.116.111
Measurement & Auto Explorer 18.104.22.16801
LaqbVIEW Run-Time 8.2.1
Have not attempted to run on another computer.
4. This is a new problem as it seemed to work before. When I first noticed the problem, it seemed to take minutes for the voltage to float up, now it occurs within seconds. I check the voltage with a multimeter directly at the breakout box on pin 34 and now it doesn't even start out at 0V when driven low. It starts out at around .11V and rises up to 1.3V in a matter of 15 seconds.
Let me know if you need any more details.
I have the DAQ board connected directly to the break-out box with no vector modulator involved and still saw the problem while running the LabWindows program. This is a program that I inherited and I've been examining more thoroughly.
I wrote my own test program in LabWindows to initialize both DAQ cards and drive all the digital outputs to 0V. When this program runs, Pin 34 starts at 0V and stays there. I let it run for 30 minutes and it was solid at 0V.
This tells me that it is the other LabWindows program that is the problem with how it initializes the DAQ cards. It uses 21 DAQ tasks for the 2 cards, not 3 as I originally thought. My test program only uses 3 tasks to set-up the cards and works. The programs use the function DAQmxWriteDigitalU8 to send the data to the DO on the DAQ cards. Is there a better description of this function than in the help?
I am looking for something that better describes what the data array should look like and how the sample settings affect the output.