With the advancement of the industrial Internet of Things, the data of RS485 multi-host communication devices in all walks of life need to be collected to the platform. But many intelligent controllers, such as PLC and frequency converter. There is only one serial interface, and there is no redundant communication interface to push the data of PLC and frequency converter to the platform acquisition gateway.The RS485 bus is a half-duplex interface, and the communication protocol is generally a rotation training mode, such as the MODBUS communication protocol. At the same time, data can only be sent or received. Then, when RS485 is used as a master station, only one device on a bus is allowed to be used as a master station, and RS485 multi-host communication devices use the bus mode for rotation training.
There are many kinds of common RS485 multi-host communication equipment, such as PLC, water meter, electricity meter, temperature controller, IO controller and transmitter from different manufacturers.
Industrial equipment is generally real-time communication, in the interface expansion, can not affect the normal communication of the original equipment, can not affect the production of equipment. What does the RS485 Ethernet to serial converter do?
The RS485 multi-host communication system does not have high requirements for the protocol. As long as it is a half-duplex communication protocol based on the RS485 bus, it can be expanded, even the half-duplex communication protocol of the RS232 interface. For example, Omron PLC communication interface supports RS232 interface, but the underlying communication protocol is half-duplex MODBUS communication protocol.
The equipment supports 485 multi-host communication;
Support multiple RS485 communication interfaces. At least three RS485 interfaces are required, one to the original slave station equipment, one to the original master station equipment, and one to the extended master station equipment.
The first step is to solve the RS485 multi-host communication. In the communication system, more than two or more devices can access the slave devices at the same time and return real-time effective data. As shown in Figure 3-1, 10 IO controllers on RS485 bus are simultaneously acquired by two computers and one industrial control panel through Shanghai Zhuolanduo Ethernet to serial converter.The data collected by the three hosts are complementary and conflicting, and they are all original data.
The second step is to solve the RS485 expansion problem. Multi-Ethernet to serial converter supports bidirectional data conversion between serial port and network. It can communicate from serial port to network or from network to serial port.
Four-channel Ethernet to serial converter solves this problem. The fourth channel is connected to the original slave station equipment, and its working mode is TCP server mode. The working mode of the first channel connected to the original master station equipment is the TCP client mode. The second channel is connected to the extended RS485 interface, and the extended interface is used by the platform gateway.
RS485 has two kinds of connections: two-wire and four-wire. The four-wire system can only realize point-to-point communication, which is rarely used now. The two-wire connection mode is mostly used now. This connection mode is a bus topology, and 32 nodes can be connected on the same bus at most.
The ideal line is twisted-pair: it is better to use one pair of twisted-pair for the two half-duplex lines, so that the two lines are twisted, and the interference level added to the two lines is offset to achieve the anti-interference effect. One pair is used for receiving two lines and the other pair is used for transmitting two lines in full duplex. RS485 has no power transmission requirements, so the requirements for wire diameter are not high.
In practical engineering, the outdoor water-blocking twisted pair is usually purchased to ensure the protection performance of the line. But some engineers will use RVV cable, which is also possible, but the anti-interference is worse. In this way, some engineers use RVVP cable (with shield), which is not good, because the increase of capacitance between lines will affect the transmission quality, and the baud rate of transmission needs to be reduced.
The setting of the baud rate has a certain corresponding relationship with the length of the cable (including the total length of the branch). The longer the line is, the lower the baud rate should be set to be more stable.
No matter what kind of cable is chosen, bus architecture should be adopted as far as possible, star connection should be reduced, branch lines should be as short as possible, and daisy-chain connection should be adopted as far as possible, that is, the bus is connected to the first node and then jumped to the next node.
1. The RS485 signal line cannot be wired together with the power line. In the actual construction, because the wiring is through the pipeline, the construction party sometimes directly ties the RS485 signal line and the power line together for convenience. Because the strong current has a strong electromagnetic signal to interfere with the weak current, the RS485 signal is unstable, resulting in unstable communication.
2. The 485 signal line may use a shielded wire or a non-shielded wire as a wiring. The 485 signal is transmitted in differential mode, that is, the voltage difference between 485 + and 485- is used as the signal transmission.
Yes, the Ethernet to serial converter can connect multiple RS485 devices. The Ethernet to serial converter is a network device that connects serial devices to the network through the TCP/IP protocol. With Ethernet to serial converter, you can remotely manage and control multiple RS485 devices for data transmission and communication.Some Ethernet to serial converter support multi-port serial ports and can connect multiple RS485 devices at the same time. In addition, some Ethernet to serial converter also support virtual serial port technology, which can simulate multiple virtual serial ports through software, thus expanding the number of RS485 devices connected.Therefore, through the Ethernet to serial converter, you can realize the connection and management of multiple RS485 devices.
