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. RS-485 electrical characteristics: logic \"1\" to the voltage difference between the two lines is (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. RS485 programming serial port protocol just defines the transmission voltage, impedance, etc., the programming method is the same as ordinary serial port programming
485 line is a communication line
485 lines are usually represented by A and B or D and D-. The logic \"1\" is represented by the voltage difference between the two lines as (0.2~6)V, and the logic \"0\" is represented by the voltage difference between the two lines as -(0.2~6)V, which is a typical differential communication
The RS485 cable can not only transmit between a single device, but also connect multiple devices on a communication bus.
RS485 adopts differential transmission mode, the transmission distance is greatly improved, the transmission distance is not limited to tens of meters, can reach more than 1200 meters.
RS485 and RS232, there is no unified interface standard, usually using DB9 interface. Sometimes, in order to facilitate wiring, you can only use two cables A and B, so RS485 has become a widely used serial communication method.