I think the Open DMX USB widget behaves as a raw serial port so you need to generate DMX packets 'manually' by sending break (sequence of zeros longer than a character) before each message. At the moment [comport] doesn't have the capability to send breaks but I think it could be done. Since the computer has to time the breaks it can happen that they are out of spec and the DMX equipment doesn't always get the messages. The Pro handles serial comms with the computer separately from the dmx so the timing is always correct.