I downloaded CSerialCom.cpp class from following link – A Simple Class for Implementing Serial Communication in Win-9X/2000 and modified it as follow to handle multiple communication ports. Here is SerialCom.h header file. #include atlstr.h class CSerialCom { // Construction public: CSerialCom(); // Attributes public: // Operations public: // Implementation public: void ClosePort(); BOOL ReadByte(BYTE &resp);