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