While, probably somewhat lateral to your current problem, please be aware that despite documentation to the contrary, the tied-handle interfaces of the Win32::SerialPort and Device::SerialPort modules are not the same - If you have a read through the source for Device::SerialPort, you will find that the TIEHANDLE subroutine calls the new method in place of the start method as what occurs in Win32::SerialPort - A convenience in Device::SerialPort which means that you do not need to have a configuration file for the serial port previously written, but one which breaks compatability with Win32::SerialPort.