This program is a demo application for BitLevelCOM software library (with full C source code) that allows a calling user application to access serial communication ports (COM devices) under 32-bit MS Windows operating systems. It allows to transmit data, receive data and control line signals (such as RTS and DTR). BitLevelCOM Library conveniently packages standard Win32 OS Communications API by providing only a few simple API services to user. Basic features: Configures serial communications COM device (Baud rate, data length, parity, stop bits); Transmits data (a single byte) to COM port with a non-blocking call; Receives data (a single byte) from COM port with a non-blocking call; Performs extended functions on COM device - Set DTR line; Clear DTR line; Set RTS line; Clear RTS line.