1. Electrical characteristics of RS-485: Logic "1" is represented by the voltage difference between the two lines as + (2-6) V; Logic "0" is represented by the voltage difference between the two lines as - (2-6) V. The interface signal level is lower than RS-232-C, it is not easy to damage the chip of the interface circuit, and the level is compatible with the TTL level, which can be easily connected with the TTL circuit.

2. The maximum data transmission rate of RS-485 is 10Mbps

3. RS-485 interface is a combination of balanced driver and differential receiver, anti-common mode dry ability is enhanced, that is, anti-noise interference is good.

4. The maximum transmission distance of the RS-485 interface is 4000 feet, which can actually reach 3000 meters, and the RS-232-C interface only allows the connection of 1 transceiver on the bus, that is, single station capability. The RS-485 interface allows the connection of up to 128 transceivers on the bus. That is, it has multi-station capability, so that users can easily establish equipment networks with a single RS-485 interface. RS-485 interface has the advantages of good anti-noise interference, long transmission distance and multi-station capability, which makes it the preferred serial interface. Because the RS485 interface consists of a half-duplex network, generally only two wires are needed, so the RS485 interface adopts shielded twisted pair transmission. The RS485 connector adopts the 9-pin connector of DB-9, the DB-9 (hole) connector of the RS485 port connecting to the intelligent terminal, and the DB-9 (pin) connector of the RS485 port connecting to the keyboard.