说明：  详细描述了RS232物理细节。 典型地，串口用于ASCII码字符的传输。通信使用3根线完成：（1）地线，（2）发送，（3）接收。由于串口通信是异步的，端口能够在一根线上发送数据同时在另一根线上接收数据。其他线用于握手，但是不是必须的。
(A detailed description of the physical details of the RS232. Typically, serial code for the ASCII character transmission. 3 lines of communication to use to complete: (1) ground, (2) send, (3) to receive. Due to the asynchronous serial communication port to send data in a line at the same time another line to receive data. Other lines for the handshake, but not necessary.)