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May 23, 2023 Why is RS485 more widely used than RS232

RS485 communication technology is used a lot in engineering, its main advantages are as follows:

Simple wiring: only need 2 wires, now generally use network cable shielded wire interface;

Communication distance is far: because of the use of differential mode communication, than RS232 communication distance is far;

Can support multi-machine networking communication: compared with RS232 only one to one connection, RS485 can mount multiple terminals online, using the query - answer way to achieve multi-machine communication;

But the serial port RS485 needs to be converted into Ethernet, that is, into TCP/IP, analysis of the reasons behind these applications are mainly:

● Ethernet can access the public network so that you can achieve long-distance communication, in the global scope to achieve monitoring, this is RS485 can not do.

When multiple RS485 ethernet converter are needed to connect to the computer, the traditional way is to use multiple serial port cards. That is to use the extension serial port on the computer to achieve multiple RS485 serial ports. After using RS485 to Ethernet serial port server, you can leave the RS485 interface to the site, and the monitoring computer this end only retain a network cable, more convenient to use.

The solution of RS485 ethernet converter

The realization of RS485 ethernet converter (that is 485 to network port), is mainly a hardware converter and a software driver. Hardware converter is divided into two kinds: serial port server (serial port networking server, serial port communication server), serial port networking module.

RS485 serial servers come with enclosures that connect existing RS485 devices to Ethernet. It is suitable for network transformation of existing RS485 serial port equipment. RS485 serial port networking module is without shell, can be understood as embedded mode of RS485 to Ethernet module, using module solution, can integrate the module into the internal user equipment, to achieve the integration of serial server and equipment. In the price of the module solution than the serial port server solution price is lower.

After using the hardware and software system of the RS485 to Ethernet solution, the user's 485 equipment is equivalent to realize the network expansion, the original hardware and software programs do not need to be modified. The hardware of serial port server has realized the conversion of RS485 interface into TCP/IP interface (network interface), so with the virtual serial port driver of the computer side can be used to convert the TCP/IP connection into a virtual serial port. Virtual serial port driver can be virtual in the computer driver layer like COM5, COM6 and other virtual serial port number, and the remote serial port server and these virtual serial port binding. In this way, when the user serial port program opens the virtual serial port, it can communicate with the remote serial port server, that is, with the serial port device.

RS485 ethernet converter implementation principle of the key technology

RS485 ethernet converter process, which contains a lot of key technologies, Ethernet technology and RS485 communication protocol need to be seamlessly combined for transition. Including: 9 bit technology, frame technology, master and slave machine mechanism.

9 bit technology: in 485 mode, the user can send 9 bits of data. And sometimes the 9th bit is used to indicate whether it is a data frame or an address frame. Since Ethernet uses 8 bits of data for network communication, there is no room for 9 bits. So how to transfer the 9 bits of 485 over becomes a problem. It is understood that Shanghai Zhuolan serial port server was used to call realcom protocol, can be RS485 9 bit data format into Ethernet 8 bit data.

Frame technology: frame is a key technology in serial port to Ethernet (including RS485 to Ethernet), that is, when the serial port server receives the data of the serial port equipment, when the data package forward to Ethernet, if each byte is played as a packet is obviously too low efficiency, then how many bytes package is appropriate. Here the user needs to set a parameter called the longest packet length and longest packet interval.

Master-slave mechanism: The master-slave technique, in which the master initializes the transmission or query, and the slave responds to the data provided by the master query. The master can communicate with the slave individually or with all the slave devices in broadcast mode.

If communicated separately, a message is returned from the device in response; If it is queried in broadcast mode, no response is made from the device.

Application characteristics of RS485 ethernet converter

Anti-interference: RS485 equipment should be as close to the bus trunk as possible, using RS485 serial port server, the bus topology can be changed to "T" topology structure, convenient site construction. If the RS485 transmission line to a certain distance, and in a complex external environment, thus prone to external interference such as electromagnetic induction of the external environment.

Stability: Differential transmission of RS485 compared with single-ended signals, differential signals reduce potential electromagnetic interference EMI, thus protecting the stability of RS485 transmission.

Extensibility: due to the extension of the RS485 bus transmission distance, or RS485 mounted equipment increase, will make RS485 signal attenuation, the RS485 ethernet converter server for relay use, can enhance and amplify the existing RS485 signal, increase the number of RS422/RS485 network RS485 equipment.

Isolation: when the distance is far from the 485 communication node between the ground plane is connected by cables (such as 485 shielded cable), the ground wire and the earth will form a ground loop, the loop will coupling external common mode noise, and produce ground loop current, may lead to the failure of the entire circuit system. Integrated RS485 isolation chip can provide isolation voltage, effective isolation, to prevent common ground interference.

RS485 is often used for long distance transmission of high data transmission rate, commonly used equipment point of sale terminal (POS), metering instruments and large special automation machines. And commonly used RS232 is now generally used in short distance transmission of low data transmission rate, in noisy environment can also work effectively, such as factories, public sites, etc., Its commonly used equipment includes low speed modems, industrial control equipment, programmable logic controller (plc), computer numerical control (CNC) machine tools, robots, embedded control computers, medical instruments and equipment and embedded controller development systems.

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