I am quite familiar with the intricacies of communication code. I have written a number of serial drivers for embedded systems over the past 20 years or so. My use of C# has been limited to writing "quick & dirty" utilities for testing my embedded systems. In this case, my code was working fine - I was just seeking a better understanding of the SerialPort class which did not behave as I expected and the Microsoft documentation for it is shallow at best. -- Regards, Ken I AM