Some lines in the domestic subway line have started to synchronize with Europe, and Ethernet communication is configured between the devices. What are the advantages and disadvantages of Ethernet communication in trains and train control buses such as MVB, CANOpen, and HDLC?
The standard of the Ethernet Communication Network (Ethernet Consist Network ECN) in the Train Communication Network (Train Communica TIon Network TCN) is specified in IEC61375-3-4-2014. The main reason for the development of this standard is that the data volume of train communication is increasing rapidly, and the traditional train bus cannot meet the transmission of large data volume. Therefore, Ethernet communication can meet the data transmission requirements. For example, car broadcast systems, video systems, download firmware programs, and so on.
Figure 1 Train TCN network type
However, due to the complexity of the physical layer, link layer and protocol stack of Ethernet itself, its reliability, network failure impact and robustness are still being verified. Therefore, the main control system of the train does not use Ethernet in large quantities. As the main control communication method. Ethernet communication and mainstream MVB, CANopen communication comparison, as shown in Table 1.
Table 1 Comparison of several communication methods of TCN
MVB bus CANopen bus real-time Ethernet
The highest baud rate is 1.5Mbps1Mbps100Mbps
Practical baud rate 1.5Mbps250kbps100Mbps
Practical communication distance less than 200 meters less than 200 meters less than 100 meters
Topology bus type, branch length less than 10cm bus type, branch length less than 6 meters switch star structure, store and forward, point-to-point communication is no more than 100 meters
Transceiver Type ESD: MAX3088
EMD: MAX3088+ isolation transformer TJA1051T (non-isolated)
CTM1051KT (isolated) Ethernet PHY chip KSZ8041NL
+Isolation transformer
Controller type MVBC02 dedicated chip
or
FPGA embedded protocol stack SJA1000T
or
MCU has its own CANDM9000
or
MCU internal Ethernet
Network node physical number 32101 to 1
Data throughput 1 node to transmit 256-bit data requires 336us1 node to transmit 256-bit data requires 1.875ms1 node to transmit 256-bit data requires 100us
The stability of the controller is very stable. It is necessary to screen the automotive-grade chip, and the program protection requires an efficient and stable protocol stack and high peripheral protection.
Time predictability can predict unpredictable and predictable
Node burst transmission may not be possible
Equipment cost is medium and cheap
Higher development costs, higher and higher
Development is more difficult and simpler
Application of key control signals in high-speed rail subway trains Low-speed low-floor vehicles and light rail control signals Communication signals that require large traffic, such as video
Maturity is very mature and mature, currently used in non-control occasions
It can be seen that the main advantage of adopting the Ethernet interface is that the transmission time can be reduced when the large data volume is transmitted, but the wiring cost and the wiring difficulty are increased, and the Ethernet communication is extremely dependent on the stability of the switch, and once the switch is dead or damaged, All nodes will not be able to communicate.
In addition, EMC (electromagnetic compatibility) also needs to be considered. Since the Ethernet rate is extremely high and its EMI (electromagnetic radiation) is extremely large, it is necessary to use a better shielded network cable.
The Ethernet interface in the train equipment includes three types: RJ45 head with locking, fiber interface, and M12 communication cable, as shown in Figure 2.
Figure 2 Ethernet interface mode
According to the "TCSN Terminal Equipment Ethernet Interface Specification" requirements, the controller Ethernet communication port access scheme is provided. At present, most of the trains use the M12 communication cable to ensure better cost performance.
The network card is generally based on the ZNE-100TL+ module of Guangzhou Zhiyuan Electronics Co., Ltd. It is easy to convert the serial port of the master MCU to an Ethernet interface.
Figure 3 Ethernet module
Features
10/100M adaptive Ethernet interface;
Supports AUTO MDI/MDIX, which can be connected by crossover cable or parallel cable;
The working mode can be selected from various working modes such as TCP Server, TCP Client, UDP and Real COM driver, and the working port, target IP address and port can be set;
Provide a common configuration function library, which is convenient for users to use VC, VB, Delphi and C++Builder to develop applications for secondary development;
Support virtual serial port working mode, provide WINDOWS virtual serial port driver, let the user serial device upgrade to Ethernet communication mode without modifying the original serial port software;
Support AT command configuration;
Support remote configuration.
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