USB to RS485 Modbus RTU Cable

USB to RS485 Modbus RTU Cable


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USB to RS485 Modbus RTU Cable


The difference and connection between modbus and rs485

RS485 is a physical interface, which is simply hardware.


MODBUS is an international standard communication protocol for exchanging data between devices of different manufacturers, generally for industrial purposes


In general, two devices transmit data through the MODBUS protocol


The relationship between modbus and rs485


Modbus was invented by Modicon (now a brand of Schneider Electric) in 1979 and is the world's first real bus protocol for industrial fields.


ModBus network is an industrial communication system, which is formed by connecting a programmable controller with an intelligent terminal and a computer through a public line or a local dedicated line. Its system structure includes both hardware and software. It can be applied to various data acquisition and process monitoring.


The ModBus network has only one master from which all communications originate. The network can support as many as 247 remote slave controllers, but the actual number of slaves supported is determined by the communication equipment used.


Using this system, each PC can exchange information with the central host without affecting each PC to perform its own control tasks.


The difference and connection between modbus and rs485


Modbus Features


(1) Standard and open, users can use the Modbus protocol for free and with confidence, without paying license fees and without infringing intellectual property rights. At present, there are more than 400 manufacturers supporting Modbus, and more than 600 products supporting Modbus.


(2) Modbus can support a variety of electrical interfaces, such as RS-232, RS-485, etc., and can also be transmitted on various media, such as twisted pair, optical fiber, wireless, etc.


(3) The frame format of Modbus is simple, compact and easy to understand. It is easy for users to use and easy for manufacturers to develop.


Smart meters were developed with the maturity of single-chip technology in the early 1980s, and now the world meter market is basically monopolized by smart meters.


The reason is the need for enterprise informatization. One of the necessary conditions for enterprises to select instruments is to have a networked communication interface.


At first, it was a simple process quantity for data analog signal output. Later, the instrument interface was RS232 interface. This interface can realize the point-to-point communication method, but this method cannot realize the networking function. The subsequent emergence of RS485 solved this problem.


rs485 features


1. Electrical characteristics of RS-485: positive logic of differential signal is used, logic "1" is represented by the voltage difference between two lines as +(2~6)V; logic "0" is represented by the voltage difference between two lines as -( 2~6) V represents.


The interface signal level is lower than that of RS-232-C, so 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. The RS-485 interface adopts a combination of a balanced driver and a differential receiver, and the anti-common mode interference ability is enhanced, that is, the anti-noise interference is good.


4. The maximum communication distance of RS-485 is about 1219m, and the maximum transmission rate is 10Mbps. The transmission rate is inversely proportional to the transmission distance. The lower the transmission rate, the longer the transmission distance. Distance, need to add 485 repeaters.


The RS-485 bus generally supports a maximum of 32 nodes. If a special 485 chip is used, it can reach 128 or 256 nodes, and the maximum can support 400 nodes.


The connection between modbus and rs485


RS485 belongs to wired transmission, so the hardware transmission medium is required. In fact, two lines are enough. The actual transmission on these two lines is the same signal, but the sender divides the signal into two, but the receiver It will restore it to the original signal, and the benefits of doing so have to be compared with RS232; RS232 also needs two wires, and more often, a ground wire is added, so it is three wires, and the ground wire is ignored. The other two only have the data signal transmitted by one line, and the clock transmitted by the other, that is, how the signal is sent from the original sender, and the receiver also does the same processing.


Therefore, the receiving end of the 485 can cancel the interference introduced by the signal during the transmission process, while the receiving end of the 232 cannot. Therefore, the 485 has strong anti-interference ability and can transmit signals over a kilometer, while the 232 can only transmit more than ten meters.


As for MODBUS, it is just a kind of communication protocol, just like Chinese and English, it is a language of communication, a language of communication between machines.


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