Digital I/O

Showing results for 
Search instead for 
Did you mean: 

Using multiple PCI-6509 cards in one PC

I am using two PCI-6509 cards in a single PC to control some digital (TTL) outputs. I use only one task to control both.
The problem is that on one of the cards that is set as the second device, when pin 34 is set low it floats from 0V to about 1.3V after about 30 seconds. This happens with either card when it is set to the second device no matter which PCI slot the cards are in. The problem only occurs when both cards are in the PC and initialized for use together.
The control is being done through a C program written using LabWindows/CVI 8.0.
0 Kudos
Message 1 of 7

Hello rich937,

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.


Chris Behnke
Sr. RF Engineer
High Frequency Measurements
0 Kudos
Message 2 of 7

Hello rich937,

This is a duplicate post. Please refer to the following post for my response. Thanks!


Chris Behnke
Sr. RF Engineer
High Frequency Measurements
0 Kudos
Message 3 of 7

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:

SW                                       Version

LabWindows                         8.0

CVI Run-Time             

NI-DAQmx                            8.3.0f3

LabVIEW                              8.0

Measurement & Auto Explorer

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.

0 Kudos
Message 4 of 7
Hello rich937,
Thank you for getting back to me with more details about your system. It sounds like the load on pin 34 might be double driving the digital line. I have a couple suggestions to try out to see if we can narrow down the specifics of this 1.3V voltage.
1. Remove the vector modulator from the equation for pin 34. Set the Digital Out to low and measure the pin. Does it behave the same and float to 1.3V ?
2. Place the vector modulator on a different pin and see if the behavior can be recreated.
3. Swap out the vector modulator on pin 34 with one from one of the other ports. Does the behavior transfer between the two or does it remain on pin 34?
4. You mentioned in your first post that this behavior only occurs when both 6509 boards are in the computer. Is the behavior there in the following situations?

 a. When both boards are installed, initialized, and all three tasks are running?
 b. When both boards are installed, initialized and tasks 1 and 3 are running?
 c. When both boards are installed, initialized, and tasks 2 and 3 are running?
 d. When both boards are installed, initialized, and only task 3 is running?

Since the behavior is the same regardless of which device you use for the third digital output task I am shying away from the device itself being damaged. Hopefully with the above suggestions we can narrow down the cause of this 1.3V constant.

I would also still suggest attempting to run this application in another computer to rule out any issues concerning the PCI bus and computer power supply.

Let me know the results.
Chris Behnke
Sr. RF Engineer
High Frequency Measurements
0 Kudos
Message 5 of 7
Thanks for the assistance - Rich

Message Edited by rich937 on 12-19-2007 01:08 PM
0 Kudos
Message 7 of 7

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.




Message Edited by rich937 on 12-19-2007 01:07 PM
0 Kudos
Message 6 of 7