I have a 2011 MBP now running Mavericks. I have a Sewell USB<->Serial I have a Trip-Lite Keyspan USA-19HS USB<->Serial and I have a Brainboxes BL-819B BT<->Serial All of them have the same issue. They can send data but do not receive data. I have a USRobotics V.92 Modem as a test and I can send AT commands to the modem and it responds. However, I only know this because I can tell the modem to go off hook and it does by the indicator lights. I never get an "OK" back from the modem. My goal isn't to use the modem, it is to control my telescope mount which is serial. I have the same issue. I can send commands to the telescope and it responds but it I never get back DEC/RA from the telescope mount. Now if I boot Windows via Bootcamp on the very same laptop then use the very same modem every thing works! Thus proving my cables and adapter are all good. I had the same problem in OS X Mtn Lion I was hoping Mavericks would fix it. But I guess not. So, does anybody have a known 100% working serial solution in Mavericks?