RS232, RS422, RS485在接线接口方面都使用DB9 9针接口，但各引脚的含义不同。各接口的引脚区别如下表描述。
| Pin | Mode | RS232 | RS422 | RS485 |
| 1 | DCD | DCD+ | - | |
| 2 | RXD | RX+ | - | |
| 3 | TXD | TX+ | D+ | |
| 4 | DTR | DTR+ | - | |
| 5 | GND | GND | GND | |
| 6 | DSR | RX+ | - | |
| 7 | RTS | RX- | D- | |
| 8 | CTS | DCD- | - | |
| 9 | - | DTR- | - |
来源：CSDN
作者：Dvorak1990
链接：https://blog.csdn.net/mozart_cai/article/details/104766913