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Why Won't My cRIO 940x DIO Module Produce the Correct Output Value?



Hardware: CompactDAQ>>Digital Input Modules>>NI 9401, CompactRIO>>Digital Output Modules>>NI 9403

Problem:

I am using a cRIO 940x module in my application and I am trying to produce an output value on a DIO line of the module. I have an FPGA I/O Node for the correct line to which I am providing a value, but I do not see this value update on the hardware.  How do I update the value correctly?


Solution:

Before writing to a digital line will have an effect, you must first set the line direction of that line to be Output.  By default, all of the DIO lines of the 940x modules have an initial line direction of Input. There are two ways to configure the line direction of these modules.
 
  1. Right-click on the specific module in the Project Explorer window and select the Properties option to display the C Series Module Properties dialog box. Select the line direction for each channel using the Initial Line Direction menu box. Save the project after the configuration is complete.
    • For the 9401 DIO Module, the channels are divided into groups of four, or nibbles. Each channel in a nibble must have the same line direction, so the channels cannot be configured in a completely independent manner. Figure 1 shows the C Series Module Properties dialog box for the 9401 module.

                                                  Figure 1. 9401 Properties Dialog Box.

    • For the 9403 DIO Module, each channel can be configured independently because the channels are not divided into nibbles. Figure 2 shows the C Series Module Properties dialog box for the 9403 module.

                                                    Figure 2. 9403 Properties Dialog Box.

  1. Alternatively, you can configure the line direction of the DIO channels programmatically. 
  • For the 9401 module, place an FPGA I/O Method Node on the block diagram and select your 9401module by right-clicking the node and using the Select Item option. Next, right-click on the node and choose Select Method»Set Line Direction.  This method will set line direction on a per-nibble basis. 
  • For the 9403 module, place an FPGA I/O Method Node on the block diagram and select the 9403 digital line or group of lines by right-clicking the node and using the Select Item option. Next, right-click on the node and choose Select Method»Set Output Enable.  This method will enable output on a per-line basis.


Related Links:
LabVIEW Help: FPGA IO Method Node
Products and Services: NI 9401
Products and Services: NI 9403

Attachments:





Report Date: 11/05/2007
Last Updated: 04/04/2012
Document ID: 4F4IMH20

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