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This article introduces the relevant knowledge of "what are the characteristics of 485 protocol". In the operation of actual cases, many people will encounter such a dilemma. Then let the editor lead you to learn how to deal with these situations. I hope you can read it carefully and be able to achieve something!

485 protocol refers to RS-485 protocol, which is the standard of serial communication; typical serial communication standards are RS232 and RS485, which define voltage, impedance and so on, but do not define software protocol.

Operating environment of this article: Windows7 system, DELL G3 computer

What does the 485 agreement mean?

485 protocol refers to RS-485 protocol, which is the standard of serial communication.

Typical serial communication standards are RS232 and RS485, which define voltage, impedance and so on, but do not define software protocols. The RS-485 bus standard specifies the electrical characteristic standard of the bus interface, that is, the definition of two logical states: the positive level is between + 2V~+6V, which represents a logical state; the negative level is between-2V~-6V, it represents another logical state; the digital signal adopts differential transmission mode, which can effectively reduce the interference of noise signal.

Characteristics

Typical serial communication standards are RS232 and RS485, which define voltage, impedance, etc., but do not define software protocols. Different from RS232, the characteristics of RS485 include:

The electrical characteristics of 1.RS-485: logic "1" is represented by the voltage difference between two wires is + (2-6) V, and logic "0" is represented by the voltage difference between two wires is-(2-6) V. If the interface signal level is lower than that of RS-232-C, it is not easy to damage the chip of the interface circuit, and the level is compatible with the TTL level, so it is convenient to connect with the TTL circuit.

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

3. The RS-485 interface is strong, that is, the anti-noise is good.

4. The maximum transmission distance of the RS-485 interface is 4000 feet, which can actually reach 3000 meters (in theory, in practice, the limit distance is only about 1200 meters). In addition, the RS-232-C interface only allows one transceiver to be connected to the bus, that is, single-station capacity. The RS-485 interface allows up to 128transceivers to be connected on the bus. That is to say, it has the ability of multiple stations, so that users can easily establish a device network by using a single RS-485 interface.

Because the RS-485 interface has good anti-noise, long transmission distance and multi-station capacity, it has become the preferred serial interface. Because the half-duplex network composed of RS485 interface generally needs only two connections, the RS485 interface is transmitted by shielded twisted pair. The RS485 interface connector adopts the 9-core plug seat of DB-9, the interface with the intelligent terminal RS485 adopts DB-9 (hole), and the keyboard interface connected with the keyboard adopts DB-9 (needle).

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