Shulou(Shulou.com)06/01 Report--

The following figure shows the design diagram of the main power supply circuit of the motherboard:

The following figure shows the design diagram of the power isolation circuit required by Ethernet, fieldbus, and 485 bus based on the main power supply.

In addition, since the power outage is also a possible single point of failure, then in the hardware architecture design, the power supply of the industrial motherboard should also consider the dual power supply circuit design! That is, redundant power. The following figure shows the design diagram of the dual standby power supply circuit for the industrial motherboard:

Therefore, the redundant power supply needs to be considered in the hardware architecture design of the industrial firewall. when one of the power supplies fails, the other power supply can still ensure the normal work of the firewall. at the same time, it is necessary to alarm the fault of the power supply within a very short time in the design, so that the maintenance personnel can maintain it in time. For the power supply technology, in addition to the design of double redundancy in the circuit, we can also use POE power supply technology.

In addition to the physical connectivity of Bypass functions and redundant design considerations on power supply, shock resistance and other performance are also very important in case of emergencies, such as external shocks, industrial firewalls can work intact and stably even if they are deliberately sabotaged by lawbreakers.

In addition, another difference between industrial firewalls and traditional firewalls is that industrial firewalls design interfaces that support industrial fieldbus protocols and RS232 or RS485 bus protocols. In the fields of industrial control, power communication, intelligent instruments and so on, serial communication is usually used for data exchange. At first, the RS232 interface is used. Due to the complexity of the industrial field, all kinds of electrical equipment will produce more electromagnetic interference in the environment, which will lead to signal transmission errors. In addition, the RS232 interface can only achieve point-to-point communication, does not have networking function, and the maximum transmission distance can only reach more than ten meters, which can not meet the requirements of long-distance communication. While RS485 solves these problems, the data signal adopts differential transmission mode, which can effectively solve the problem of common-mode interference, the maximum distance can be up to 1200 meters, and allows multiple transceiver devices to be connected to the same bus. With more and more industrial application communication, Schneider Electric formulated a bus protocol Modbus protocol for industrial field in 1979. Now Modbus protocol is used in many industrial communication occasions when RS485 is used. Therefore, in the case of RS485 communication, the industrial firewall must also support the protection based on the RS485 bus protocol. In order to support the RS485 bus protocol, a serial port module must be added to compile the RS bus interface circuit design diagram, as shown in the following figure is a typical RS485 bus circuit design diagram:

In the past, PC communicates with intelligent devices by means of RS232, RS485, Ethernet and so on, which mainly depends on the interface specification of the device. However, RS232 and RS485 can only represent the physical media layer and link layer of communication. if we want to realize two-way access to data, we must write communication applications by ourselves, but most of these programs can not meet the specifications of ISO/OSI, and can only achieve a single function, which is suitable for a single device type, and the program is not universal. In the equipment network of RS232 or RS485 equipment, if the number of devices exceeds 2, RS485 must be used as the communication medium. The exchange of information between devices in RS485 network can only be realized through the transfer of "master (Master)" devices, which is usually PC, but only one master device is allowed in this kind of equipment network, and the rest are all Slave devices. Fieldbus technology is based on ISO/OSI model and has a complete software support system, which can solve the problems of bus control, conflict detection, link maintenance and so on. Fieldbus devices are automatically netted, and there is no master / slave device or multi-master is allowed. At the same level, the products of different manufacturers can be interchangeable, and the devices are interoperable. CAN protocol is the representative and most widely used protocol of this kind of fieldbus protocol. CAN-Bus (Controller Area Network), namely controller local area network, is one of the most widely used fieldbuses in the world. At first, CAN-bus was designed as a communication between microcontrollers in the automobile environment, exchanging information between the ECU of the electronic control devices on the vehicle, and forming an automobile electronic control network. It is a kind of multi-master serial communication bus. The basic design specification requires high bit rate, high anti-interference, and can detect any errors. When the signal transmission distance reaches 10Km, it can still provide a data transmission rate as high as 5Kbps. Because of these characteristics, CAN serial communication bus is naturally widely used in automobile, manufacturing and aviation industries. Because of the extensive application of CAN fieldbus protocol and its position in the industrial environment, the design of industrial firewall must also consider its support. The following figure shows the implementation circuit of the fieldbus protocol driver design of the industrial firewall on the motherboard, which is divided into the driver chip and the control chip.

Summary: based on the industrial firewall, first of all, we need to meet the hardware requirements of the industrial environment, and the hardware design must be designed in accordance with industrial standards; at the same time, we also need to consider the industrial requirements for real-time network processing. Hardware design has to consider using a more reasonable processing architecture to achieve real-time packet processing faster at the hardware level. In addition, based on the stability requirements of the industrial level, the industrial firewall should also consider the design of Bypass bypass protection and two-way power supply to meet the stability requirements as far as possible. In addition, the high-availability HA function of the industrial firewall itself must also be considered. According to most of the firewall designs investigated at present, most of them are implemented at the software level, and few are based on the hardware level to achieve the highly available functions of the equipment.

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