| DB9 pin type | RS-232 port (female/female) | RS458 half duplex | RS422 full duplex |
|---|---|---|---|
| 1 | Empty N\A | RS485（A+） | Send TXD (A+) |
| 2 | TXD | RS485（B-） | Send TXD (B-) |
| 3 | RXD | Empty N\A | Acquire RXD (A+) |
| 4 | Empty N\A | Empty N\A | Receive RXD (B-) |
| 5 | Ground GND | Ground GND | Ground GND |
What is UART
UART is Universal Asynchronous Receiver/Transmitter (Universal Asynchronous Receiver/Transmitter), commonly referred to as UART, is an asynchronous transceiver transmitter, and is a key module for asynchronous communication between devices. As long as the communication parties adopt the same frame format and baud rate, the communication process can be completed with only two signal lines (Rx and Tx) without sharing the clock signal, so it is also called asynchronous serial communication .