Thanks for your response, but it appears to indicate that you didn't really understand the question. The CP2103 I referred to is an active device, which converts USB data to GPIO pins, not just a simple cable. I am no expert on USB protocol, but I believe that messages have a target address embedded within them. Hence, the Guidemaster software must have a target address to which it send the RA and Dec commands. I simply wanted to ask if anyone knew what it was, so that I could program the CP2103 accordingly.