Using cFP-2120 controller and Labview 8.2 with cFP-DO-401 module.
After set up with MAX, using Digital Output.vi from examples directory.
The VI works fine with changing states ON/OFF.
The green state indicator lights on the module illuminate when on and go out when off.
Using 24Vdc supply.
According to the manual, we should receive 23.85V differential between V(SUP) and V(OUT).
Receiving 0V differential.
According to the manual, there should be a an effective resistance between V(OUT) and V(SUP) of 0.3 Ohms when in the ON state. We receive 2-3MOhms (open) effective resistance in both ON and OFF states.
Did you make connection between an external supply and cFP-DO-401? This module has optical isolation built in. That means that an external supply has to be used to power the module outputs. The LED's you are seeing are on the controller side of the isolation and are powered by the controller.