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Research on the technology of RS485 over Ethernet Abstract—RS485 Bus is adopted in part of communication structure in the process of remote control communication. Different RS485 communication line is difficult to integrate due to different control systems and communication protocols. Based on this, this paper presents a method which can integrate the original RS485 communication line together without damaging the existing RS485 communication structure,that is the technology of RS485 over Ethernet .The above technology not only avoids multiple RS485 lines but also implements the access based on IP. Keywords-Ethernet; RS485; remote control; multiplexing 70364
I. INTRODUCTION Taking into account safety and their own development industrial and mining enterprise are all equipped with remote control system.Most adopt RS485 Bus[1] to communicate in the remote control process system.Variety of RS485 control systems coexist in a enterprise during the development due to different control parameter and mode.It’s difficult to transmit the signal by a data line because of different communication protocol[2-3] for specific devices. This leads to poor system compatibility and scalability, line maintenance is also very difficult.Based on this,the paper presents a technology which can transmit multiple serial data by TCP/IP.The technology is on basis of Ethernet and don’t need to damage the original RS485 constructure.By this way,it not only resolves the problem of communication distance, communication speed and multi-protocols, but also greatly improve the reliability of data communications, security, realizes Internet data access across the serial port and no dormain.
II. RS485COMMUNICATION STATUS RS485 is a standard based on RS422, RS232 set by EIA.In the standard multi-point and bidirectioncommunication, capability is added,multiple transmitters is allowed to be connected together, the transmitter drive capability and conflict protection features is enhanced at the same time,Bus common mode range is expanded. It uses a balanced transmission and differential reception to complete communications, which has strong common mode interference ability. Transmission rate and transmission distance is functional relation.It works for half-duplex, supports multi-point data communications, but does not support ring or star network. Its topology is generally a terminal matched Bus structure with less cable, thus communication is easy.The mode is pided into master-slave and alternative master-slave mode as follows: A. Master-slave mode The entire communication system is consist of a master node and several slave nodes. Master node constantly check whether the salve node needs to communication, if it needs then give the right of Bus control to the slave nodes until data is sent completely.That is the master device can initialize the transmission, slave device makes some response according to data provided by the master query. Master device not only may communicate with slave separately, but also can broadcast data.If the slave devices want to communicate with each other which must through the master device. 论文网
B. Alternative master-slave mode The mode means delivering the Bus control on all nodes in a similar way like Token Ring, the node which gets control right becomes master node, other nodes are slave nodes. A node passes the Bus control to the adjacent nodes when it finished sending data, and that adjacent nodes passed down the control right after dealing with itself communication requirements.So any control point can initialize communication with other controller. Master-slave structure is widely used in the RS485 remote process control communication system,which is shown as Fig.1. Different control system's manufacturer designs different control parameters and communication protocol format so that each manufacturer laying its own cables. The result is industrial and mining enterprises have many such independent system structure whose maintenance is more difficult and the line can not be multiplexed.
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