Just a note to provide status: Little or no progress to date. Unable to determine the serial port settings on Windows application. Windows application is reliable and consistent. Chirp code can get the radio to respond with ID about %75 of the time but that does not translate to reliable. Processing beyond ID acquisition does not yield proper responses from the radio. Therefore, I guess that the handshake/protocol of the radio is not being understood by me. I have confirmed the proper hex string is being sent to the radio but the radio does not respond as it does with the Windows program. I tried different sleeps with no success. So, now I am reverting back to stage one. Since the radio does not act reliably as with Windows, I assume that the serial settings are not a match. Secondly, the Windows program closes and re-opens the serial port before communicating with the radio. I am assuming that it is setting non-default parameters on the serial port. My current plan of diagnosis is to try various settings to see if there is a problem there. Unfortunately, I am stuck trying to set the parity. All other parameters seem to be accepted except that one. Any advice? 73, Alan - W6ARH