Salam Payam,

I saw the post where you asked about DTR and RTS. I wanted to respond because the first time I hooked up a microprocessor this bothered me too.

You do not need to do anything with any of the handshaking lines on a UART. The only lines you need to use are Tx, Rx, and GND. All of those other lines (data terminal ready, request to send, clear to send, whatever, etc.) can be ignored.

I know. It just doesn't seem right does it. But think about what UART stands for. Universal Asynchronous Receiver Transmitter. The important part is "asynchronous." The driver that handles your COM port has a buffer to take care of whatever it receives independently of whether anything is being transmitted. The handshaking coordination is simply unnecessary.

That isn't to say you won't use some software protocol if need be. And you might use XON/XOFF as a means of flow control. But you do not need all of those other lines on the serial port.

Hope this helps. Good Luck.