What Is RS-485?

The RS485 electrical standard has undergone the development of two standards, RS232 and RS422. It inherits most of the characteristics of RS422, and also has networking functions that RS232 does not have. Compared with the other two standards, the equipment performance of the RS485 standard has been greatly improved. One driver can drive at least 32 receivers. The higher the impedance, the more receivers can be driven. Under normal circumstances, each device will only turn on the line driver during data transmission, and under its high impedance state, the driver will stop working to ensure that other devices can perform normal data transmission.

RS-458

The RS485 electrical standard has undergone the development of two standards, RS232 and RS422. It inherits most of the characteristics of RS422, and also has networking functions that RS232 does not have. Compared with the other two standards, the equipment performance of the RS485 standard has been greatly improved. One driver can drive at least 32 receivers. The higher the impedance, the more receivers can be driven. Under normal circumstances, each device will only turn on the line driver during data transmission, and in its high impedance state, the driver will stop working to ensure that other devices can perform normal data transmission.

Many devices on the market now have RS485 interfaces, such as optical transceivers. This kind of equipment has the function of changing the communication standard, which can realize the optimization of performance. For example, the RS23 / RS485 converter can convert a full-duplex RS232 network to a half-duplex RS485 network.

Chinese name

RS-485

Classification

Proper noun

Part of speech

noun

Language

English

What is the RS-485 interface? What are its characteristics compared to the RS-232-C interface?

Since the RS-232-C interface standard appeared earlier, it is inevitable that there are deficiencies, mainly including the following four points:

(1) The signal level of the interface is high, which can easily damage the chip of the interface circuit, and because it is incompatible with the TTL level

Therefore, it is necessary to use a level conversion circuit to connect with a TTL circuit.

(2) The transmission rate is low. During asynchronous transmission, the baud rate is 20Kbps.

(3) The interface uses a signal line and a signal return line to form a common ground transmission form. This common ground

The transmission is prone to common mode interference, so the anti-noise interference is weak.

(4) The transmission distance is limited. The standard value of the maximum transmission distance is 50 feet. In fact, it can only be used at 50 meters.

about.

In response to the shortcomings of RS-232-C, there have been some new interface standards. RS-485 is one of them.

First, it has the following characteristics:

1. Electrical characteristics of RS-485: logic "1" is represented by the voltage difference between the two wires being + (2-6) V;

Logic "0" is represented by the voltage difference between the two lines as-(2-6) V. Interface signal level ratio RS-232-C

Lowering, 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

TTL circuit connection.

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

3. The RS-485 interface is a combination of a balanced driver and a differential receiver, which enhances the ability to resist common mode interference.

That is, anti-noise interference is good.

4. The standard value of the maximum transmission distance of the RS-485 interface is 4000 feet, which can actually reach 3000 meters.

The RS-232-C interface allows only one transceiver to be connected on the bus, which means single station capability. The RS-485 interface is

Up to 128 transceivers are allowed on the bus. I.e. multi-station capability, so users can use a single

RS-485 interface makes it easy to set up a device network.

Because the RS-485 interface has good anti-noise interference, the long transmission distance and multi-station capability make it the preferred serial interface. Because a half-duplex network consisting of an RS485 interface generally requires only two wires, the RS485 interface uses shielded twisted pair transmission. The RS485 interface connector uses a DB-9 9-pin plug socket, the RS485 interface with the intelligent terminal uses DB-9 (hole), and the keyboard interface RS485 with the keyboard uses DB-9 (pin)