What does 485 agreement mean?

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

The operating environment of this article: Windows 7 system, DELL G3 computer

What does the 485 protocol mean?

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

Typical serial communication standards are RS232 and RS485, which define voltage, impedance, etc., but do not define the software protocol. The RS-485 bus standard stipulates the electrical characteristic standards of the bus interface, that is, the definition of two logical states: the positive level is between 2V and 6V, indicating a logical state; the negative level is between -2V and -6V, which means Another logical state; the digital signal adopts differential transmission method, which can effectively reduce the interference of noise signals.

Features

Typical serial communication standards are RS232 and RS485, which define voltage, impedance, etc., but do not define the software protocol, which is different from RS232 and RS485 The characteristics include:

1. Electrical characteristics of RS-485: Logic "1" is represented by the voltage difference between the two lines (2-6) V; logic "0" is represented by the voltage difference between the two lines. It is expressed as -(2-6)V. The interface signal level is lower than RS-232-C, which makes it less likely to damage the chip of the interface circuit. Moreover, the level is compatible with the TTL level and can be easily connected to the TTL circuit.

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

3. The RS-485 interface is strong, which means it has good anti-noise interference.

4. The standard value of the maximum transmission distance of the RS-485 interface is 4000 feet, which can actually reach 3000 meters (theoretical data, in actual operation, the limit distance is only about 1200 meters). In addition, RS The -232-C interface only allows one transceiver to be connected to the bus, that is, single station capability. The RS-485 interface allows up to 128 transceivers to be connected to the bus. That is, it has multi-station capability, so users can easily establish a device network using a single RS-485 interface.

Because the RS-485 interface has good anti-noise interference, long transmission distance and multi-station capability, it has become the preferred serial interface. Because a half-duplex network composed of an RS485 interface generally only requires two connections, the RS485 interfaces all use shielded twisted pairs for transmission. The RS485 interface connector uses a DB-9 9-pin plug socket, the RS485 interface with the smart terminal uses DB-9 (hole), and the keyboard interface RS485 connected to the keyboard uses DB-9 (pin).

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