Connect NI 73XX DIO to 3rd Party Equipment

Updated Oct 30, 2018

Reported In


  • Motion Controller Device


  • NI-Motion

Issue Details

When I connect digital outputs from the NI 73xx controllers through a Universal Motion Interface (UMI) in order to move a motor, disable a drive, or trigger an event, the signal at the motion controller will change. However, my third-party drive will not generate any of these actions. Why is this?


By default, the breakpoint, inhibit, and step & direction output signals on the NI 73xx controllers are configured as 'open collector.' Open collector means that the controller can sink a fairly large amount of current, but source very little.

A popular way to provide optical isolation for the digital inputs on many third party amplifiers is by means of an optocoupler. In order to operate properly, an optocoupler requires that the signal that will switch its state provide enough current to do so. In a scenario where the two previous circumstances are present, the effect may sometimes be that the NI 73xx controller sends out a breakpoint, inhibit, or step & direction signal, and the third party equipment will not see any transition at all. The drive will produce no response to the command. In order to properly connect the inhibit, step, and direction lines, please refer to this Knowledgebase: How do I get the 73xx controller and UMI-7764 to drive a third party stepper motor.

The breakpoint outputs on the 733x and 734x controllers are also open collector. On the 735x however, the breakpoint output signals may be configured either as open collector or totem pole by selecting their mode in Measurement and Automation Explorer like the picture below by following these steps:
1. Open Measurement and Automation Explorer.
2. Under Devices and Interfaces, Locate your 735x series controller.
3. Expand Default 7350 settings.
4. Expand Axis X (where X is the desired axis).
5. Click on Compare and Capture Settings.
6. Under Position Breakpoints, select either Open Collector or Totem Pole.
7. Click Save and then Initialize.

If you are using open collector mode breakpoints, the connections to optocoupled trigger inputs on third-party equipment should follow the same rules described in section 1 of the tutorial for all open collector signals. If you are using totem pole mode breakpoints, then these connections should follow the same rules described in section 2 of the tutorial for all totem pole signals.


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