I have a project with an atmega using the serial port. I have a max3232 logic level converter for RS232. I communictate fine with some PC software I am using and have used a few different PCs without difficulty. I tried connecting it to a PDA serial port and the PDA recieves the status packets once per second like expected, but when I open and close the serial port on the pda it causes the microcontroller to go into some unknown state. I can't even communicate with it when I reconnect the device to a PC. Once the device is reset it performs as expected again with the PC. This problem is repeatable. It's as if the PDA is causing some glitches and screwing up the firmware. It is wierd because the firmware checks packets using a crc and packet headers.