串口RS232引脚定义

1 逻辑电平

EIA-RS-232C 对电器特性、逻辑电平和各种信号线功能都作了规定。

在TxD和RxD上：

逻辑1(MARK)=-3V～-15V

逻辑0(SPACE)=+3～+15V

在RTS、CTS、DSR、DTR和DCD等控制线上：

信号有效（接通，ON状态，正电压）＝+3V～+15V

信号无效（断开，OFF状态，负电压)=-3V～-15V

2. 引脚定义

针脚 定义 符号

1 载波检测 DCD           Pin 1 Received Line Signal Detector(Data Carrier Detect)

2 接收数据 RXD           Pin 2 Received Data

3 发送数据 TXD           Pin 3 Transmit Data

4 数据终端准备好 DTR   Pin 4 Data Terminal Ready

5 信号地 SG                Pin 5 Signal Ground

6 数据准备好 DSR        Pin 6 Data Set Ready

7 请求发送 RTS           Pin 7 Request To Send

8 清除发送 CTS           Pin 8 Clear To Send

9 振铃提示 RI             Pin 9 Ring Indicator

3. 9针和25针串口引脚对应关系

4  连线方法

Usually Not. While the normal PC hardware might well run with just Tx, Rx and Ground connected, most driver software will wait forever for one of the handshaking lines to go to the correct level. Depending on the signal state it might sometimes work, other times it might not. The reliable solution is to loop back the handshake lines if they are not used.

Handshake looping a PC serial connector

http://airborn.com.au/serial/rs232.html

5  串口RS232数据帧格式

在串口的总线上，高电平是默认电平，当一帧数据开始传输时，必须先把总线拉低一位作为起始位