Configuring NI 6xxx Devices for Wired-OR (Open Collector) Output Mode In LabVIEW

Updated May 3, 2018

Reported In

Hardware

  • USB-6001

Software

  • Measurement & Automation Explorer (MAX)

Driver

  • NI-DAQmx

Issue Details

  • How do I configure my NI 6xxx devices to be in wired-OR (Open Collector) output mode?
  • Can I configure set the digital output modes to open collector via NI-Measurement and Automation Explorer (MAX)?

Solution

To configure a digital line for output in wired-OR mode in Traditional NI-DAQ, do the following:
  1. Call the DIO Port Config VI.
  2. Set the line direction for that bit to be 1 (-1 to set all the lines in a port to output).
  3. Configure that line for wired-OR mode by also setting the same bit(s) in the wired OR map to be 1. 
To configure a digital line for output in Open Collector mode in DAQmx, do the following:
  1. Call the DAQmx Create Virtual Channel and set it to Digital Output
  2. Add a DAQmx Channel Property node and select the Digital Output»OutputDriveType property. 
  3. Set the drive type to be Open Collector 
This property is not available to configure in NI MAX. 
 

Additional Information

Wired-OR mode and Open Collector mode will both provide the same functionality for the Digital Output lines when the outputs of the Open Collector are tied together. Wired-OR mode is defined in Traditional NI-DAQ and Open Collector mode is defined in DAQmx. Once a line is configured for wired-OR (Open Collector) mode, writing a 0 to the line will set the line low and writing a 1 to the line will set the line into a high impedance mode (does not drive a voltage). You can connect DPULL to +5V (which provides a 100kOhm pull-up resistor on all data lines) to determine the state of the line when it is high impedance.

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