串行直连电缆 9针-25针(NullModem)
串行直连电缆用于两台计算机的直接相连，电缆两头的插头一头是 9 针母插头，另一头是 25 针母插头：
|
引脚界说 |
| D-Sub 9 | D-Sub 25 |
|
|---|---|---|---|
|
Receive Data |
2 |
2 |
Transmit Data |
|
Transmit Data |
3 |
3 |
Receive Data |
|
Data Terminal Ready |
4 |
6+8 |
Data Set Ready + Carrier Detect |
|
System Ground |
5 |
7 |
System Ground |
|
Data Set Ready + Carrier Detect |
6+1 |
20 |
Data Terminal Ready |
|
Request to Send |
7 |
5 |
Clear to Send |
|
Clear to Send |
8 |
4 |
Request to Send |
