|     9针接口针脚定义 Pin 1 Received Line Signal Detector  (Data Carrier Detect)
 Pin 2 Received Data
 Pin 3 Transmit Data
 Pin 4 Data Terminal Ready
 Pin 5 Signal Ground
 Pin 6 Data Set Ready
 Pin 7 Request To Send
 Pin 8 Clear To Send
 Pin 9 Ring Indicator
 
 RS232接口针脚定义
 25针的接口定义:
 Pin 1 Protective Ground
 Pin 2 Transmit Data
 Pin 3 Received Data
 Pin 4 Request To Send
 Pin 5 Clear To Send
 Pin 6 Data Set Ready
 Pin 7 Signal Ground   Pin 8 Received Line Signal Detector
 (Data Carrier Detect)
 Pin 20 Data Terminal Ready
 
 接线说明
 1.DB9和DB25的常用信号脚说明
 
 9针串口(DB9)             25针串口(DB25)
 
 针号功能说明       缩写     针号功能说明     缩写
 1    数据载波检测   DCD      8    数据载波检测 DCD
 2    接收数据       RXD      3    接收数据     RXD
 3    发送数据       TXD      2    发送数据     TXD
 4    数据终端准备   DTR      20   数据终端准备 DTR
 5    信号地         GND      7    信号地       GND
 6    数据设备准备好 DSR      6    数据准备好   DSR
 7    请求发送       RTS      4    请求发送     RTS
 8    清除发送       CTS      5    清除发送     CTS
 9    振铃指示       DELL     22   振铃指示     DELL
 
 2.RS232C串口通信接线方法(三线制)
 
 9针-9针 25针-25针 9针-25针
 2  3  3   2   2  2
 3  2  2   3   3  3
 5  5  7   7   5  7
 
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