Zhou,
Take a look to one of the examples shipped with LabVIEW, Help > Search Examples... > I/O Interfaces > Data Acquisition (DAQ) > Digital Input and Output > Immediate Digital Input and Output > and select the example named "Write to One Digital Port on an E Series Device"... this one should work with your board, and you select port 3 to work on... try switching the line state...
In conclusion.... if you are using binary representation in your pattern, then your least significant bit (right-most bit) is going to be 3.0, then the next bit to the left will be 3.1, and so on... run the example so you can see this... so whatever the port number is, always your far most right bit is your line 0 of the port...
Good luck!...
Nestor Sanchez
Applications Eng
ineer
National Instruments
Nestor