USB interface with non standard OS

I want to connect the Arduino Micro (which has the same USB-Interface as the YUN) with a Real-Time OS without USB-driver. The OS (Real-Time Labview) sees the Arduino as 3 Ports, one with input and output pipe, but I get no data from the arduino (which I programmed to send data to the serial port).
Other USB interfaces simulating a simple com-port work nicely with this OS.
Do I have to send special commands to the interface to enable data transportation? Is there any information what the windows driver does to simulate a serial device?

Best regards