Application and scheme of RS485 to Ethernet transmission

Application and scheme of RS485 to Ethernet transmission

1. RS485 to Ethernet application

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

The wiring is simple: only 2 wires are needed, and now the shielded wire interface of the network cable is generally used.

Long communication distance: Due to the use of differential mode communication, the communication distance is longer than RS232.

Support multi-machine network communication: Compared with RS232 which can only connect one-to-one, RS485 can mount multiple terminals online, and realize multi-machine communication by query-response.

However, RS485 now often needs to be converted to Ethernet, that is, converted to TCP/IP. The main reasons behind the analysis of these applications are:

Ethernet can be connected to the internet so that it can realize long-distance communication and realize monitoring on a global scale, which is not possible with RS485.

When multiple RS485 devices are needed to connect to the computer, the traditional way is to use a multi-serial port card, that is, use the extended serial port on the computer to implement multiple RS485 serial ports.

After using RS485 to Ethernet, you can leave the RS485 interface on site, and only one network cable can be reserved at the monitoring computer end, which is more convenient to use.

2. RS485 to Ethernet solution

The realization of RS485 to Ethernet (ie, 485 to network port) is mainly a hardware converter and a software driver.

There are two kinds of hardware converters: serial port server (serial port networking server, serial port communication server), serial port networking module.

The RS485 serial server is with a shell, which can connect existing 485 devices to the Ethernet.

It is suitable for the network transformation of the existing RS485 serial port equipment.

The RS485 serial port networking module does not have a shell. It can be understood as an embedded RS485 to Ethernet module. Using a module solution, the module can be integrated into the user's device to realize the integration of the serial server and the device.

The price of the module solution is lower than that of the serial server solution.

After using the hardware and software system of the RS485 to Ethernet solution, the user's 485 device is equivalent to the realization of network expansion, and the original hardware and software programs do not need to be modified.

The hardware of the serial server realizes that the RS485 interface is converted into a TCP/IP interface (network interface), then the TCP/IP connection can be converted into a serial port virtually again by using the virtual serial port driver on the computer side.

The virtual serial port driver can virtualize the virtual serial port numbers like COM5, COM6, etc. in the driver layer of the computer, and bind the remote serial server to these virtual serial ports.

In this way, when the user serial port program opens the virtual serial port, it can communicate with the remote serial server, that is, communicate with the serial device.

3. The key technology of RS485 to Ethernet

If RS485 is to be seamlessly upgraded to Ethernet, it contains many key technologies. It is necessary to seamlessly combine Ethernet technology and RS485 communication protocol for transition.

Including: framing technology, 9-bit technology, master-slave mechanism, etc.

Now focus on the framing technology, and briefly explain it.

Framing technology: Framing is a key technology that appears in serial to Ethernet (including RS485 to Ethernet), that is, when the serial server receives data from the serial device, when will the data be packaged and forwarded to the Ethernet, if every It is obvious that the efficiency is too low if all bytes are packed into one packet. So how many bytes are suitable for packing, here needs the user to set a parameter called the longest data packet length and the longest data packet interval.