I currently have a computer controlled stimulator (usb driven). So when I send specific bytes it stimulates with the intensity and pulse width contained in the data sent. Basically I want to monitor the usb connection with the arduino uno connected in between the computer and device. Then if a certain byte is sent I want change a digital pin on the arduino from low to high. From what I have read it seems the tx/rx pins can be used to transmit data but not sure they are directly connected to the usb connector.
Hope this makes sense.