characteristics
Typical serial communication standards are RS232 and RS485, they define the voltage, impedance, etc., but do not define the software protocol, different from RS232, RS485 features include:
1. Electrical characteristics of RS-485: logic \"1\" is represented by the voltage difference between the two lines as (2-6) V; The logical \"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 interference ability is enhanced, that is, anti-noise interference is good.
4. The maximum transmission distance of the RS-485 interface is 4,000 feet (about 1219 meters), which can actually reach 3,000 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 half-duplex network composed of RS485 interfaces generally requires only two connections, the RS485 interface adopts shielded twisted pair transmission. The RS485 port connector uses the 9-pin connector of the DB-9, the DB-9 (hole) port of the RS485 port connected to the smart terminal, and the DB-9 (pin) port of the RS485 port connected to the keyboard.