Hi Rick - you may need to download a driver. I know, in the case of my Moonlite focuser, I had to download a driver to my Mac to get them to talk. In that case Moonlite provides the following link: ftdichip.com/drivers/vcp-drivers/. I notice on that FTDI page they have a link to "D3XX Drivers" and there you can find drivers for a Mac. I'm only suggesting this since D3XX looks suspiciously like it might fit in with the D309 driver that worked for me. I'm not a programer or super knowledgeable in USB/serial connections - just providing this if it helps. Perhaps others will have more educated inputs for you. I've had to download serial drivers for Celestron mounts as well.