How do you properly ground a digital output signal?

[Chem Lab]

I'm trying to properly ground several digital output signals. I have the following components:
NI PCI-6221 Part# 779066-01 (DAQ Board)

CB-68LPR Part# 777145-02 (I/O Connector Block)

SHC68-68-EPM Part# 192061-01 (Noise Rejecting, Shielded Cable)

I have a single digital ground connected for multiple digital output signals. Will this properly ground them? It doesn't seem to be properly grounding the output signals. Is there a way I can configure a digital ground for a single digital output? I couldn't find any way to do this in MAX? Are there any other suggestions? Thank you for all of your help.

Kathleen

[Salvador_Santolucito]

Hi,

Check out the M series help manual: http://digital.ni.com/manuals.nsf/websearch/9477D6DF1FE5A72986256FAB00633DE4?opendocument

In there you can look in the index for "digital I/O." In the digital section you will find a circuit diagram for how to connect inputs and outputs to your DIO lines. Basically, all of your lines are referenced to D_Gnd.


-Sal

[Chem Lab]

Thanks, but which digital ground should I connect, there's about 10 different digital grounds. Is there specific ones designated for specific channels? Do I physically have to connect the digital ground pin to the digital channel it goes to? This is where I was confused. Thanks again.
Kathleen

[Salvador_Santolucito]

Hi,

It doesn't really matter. They are all tied together within the board. I usually recommend to connect it to the D_Gnd pin that is closes (physically closest on the connector) to the pin you are outputting on.

-Sal

[Chem Lab]

I actually have a second question, that maybe you can help me with then. I'm trying to send a ttl pulse through these digital outputs. When I open Measurement and Automation Explorer, and test the outputs through this means, it seems to work, but the output signal never stops. Now when I try to use LabView 7.1 to send the same pulse, it doesn't seem to be able to do anything, I looked at the Digital Pulse Example, but for some reason it still doesn't work. Do you have any suggestions? I don't understand how this would work for a specific task in MAX and not in LabView? Thanks again.
Kathleen

[Salvador_Santolucito]

Hi,

When you update the digital lines they will hold their states until they are updated again. That means that you can set the bits in MAX and they will keep their states until you re-write them.

The LabVIEW examples should work. Are you using a DAQmx shipping example?

They are in LabVIEW under Help >> Find Examples >> Hardware Input and Output >> Digital Generation >> Write Dig Chan

If you are using one of the "Generating Digital Pulses" examples then you are not actually using your DIO lines. The "digital pulse" examples are actually used for generating pulse trains through the counter output pins (not DIO lines).

-Sal

[Chem Lab]

Hi again, and your last message was tremendously helpful. Unfortunately I can't figure out which data input I should use into the DAQmx Write SubVI, I used the Boolean single line SubVI. I tried a simple Boolean true constant input and this didn't seem to work. Do you know how I should try to determine the appropriate input for my application? I looked at the help menu but it wasn't very helpful for the data input. Thanks again.
Kathleen

[Salvador_Santolucito]

Hi,

Check out my attached picture. It shows how to input different data types into the DAQmxWrite.

-Sal