With the rapid development of Ethernet technology and its increasingly widespread application in commercial fields, more and more industrial control equipment is gradually using Ethernet and adopting the TCP/IP protocol as the main communication standard. Although the Ethernet standard used in industrial control is the same as that in commercial Ethernet, industrial control requires networks to operate stably in harsher environments. Therefore, network products used to connect industrial equipment need to be specially designed to provide industrial-grade reliability to meet the needs of long-term continuous operation. Furthermore, in industrial control, the devices to be connected are often geographically dispersed, with few devices connected in a single location. This creates a significant demand for 8-port fiber optic network switches that support fiber optic redundant loops. To achieve fiber optic redundant loop functionality, high-performance microprocessors are needed for network management and control, and high-performance network switching chips are required to implement basic 10/100M Ethernet switching functions.
The following section mainly introduces the software and hardware design concepts of an industrial Ethernet switch with a CPU using a 32-bit ARM core microprocessor, six 10/100M twisted-pair ports and two 100M fiber optic ports, and capable of implementing redundant loop functions.
1 Hardware Design
The hardware of a fiber optic loop industrial Ethernet switch is mainly divided into two modules: the CPU module and the switching module. These two modules will be described in detail below.
1.1 CPU Module
The CPU module can be divided into two parts: the power supply section and the CPU and peripheral circuit section. The block diagram is shown in Figure 1.
The MAX788 is a switching Zener diode with an output voltage of 3.3V, a maximum output current of 5A, an input voltage range of 8V to 40V, and an internal switching frequency of 100kHz.
The switch uses Atmel's AT91M40800 32-bit ARM core microprocessor chip for CPU and a high-speed 256K×16-bit RAM Cy7C1041BV33 for RAM.
The 29W400 FLASH memory is used to store programs and some configuration information; its capacity is 256K×16 bits. The AT91M40800's serial port expands to an RS-232 interface, allowing the PC to directly manage and configure the switch via this interface. The MAX823 is a power monitoring chip with watchdog functionality, providing a reliable reset signal.
The CPU module and the switching module are connected via a 40-pin connector, primarily for setting registers and reading/writing network data to the switching chip. The JTAG port enables real-time emulation of the AT91M40800 and for downloading programs to the FLASH memory.
1.2 Switching Module
The switching module mainly consists of the MAX layer main switching chip VT6510B and the physical layer chip RTL8208. The main switching chip is the VT6510B manufactured by VIA Technologies. This chip has nine 10/100M ports and one 1G port, and embeds 384KB of control RAM and packet switching buffer RAM, enabling it to perform complete switching functions. It also provides a host interface so that an external CPU can initialize and manage this switching chip.
Eight 10/100M ports are connected to the Realtek RTL8208 physical layer chip via RMII interfaces. The RTL8208 chip integrates eight physical layer ports, which can be configured to use either 10/100BASE-TX (twisted-pair interface) or 100BASE-FX (fiber optic interface). This system uses six 10/100BASE-TX ports and two 100BASE-FX ports. The six 10/100BASE-TX ports need to be connected to the RJ-45 interfaces via an HR604009 isolation transformer, which provides four RJ-45 interfaces. The two 100BASE-FX ports can be directly connected to the V23826 fiber optic transceiver, which provides a single-mode SC interface.
In addition, the physical layer chip RTL8208 can display the status of each network port through an external LED output via a serial shift register 74HC164.
Since the core operating voltage of VT6510B and RTL8208 is 2.5V, a low-dropout voltage regulator chip MAX1818 is also needed to reduce the voltage from 3.3V to 2.5V.
The principle block diagram of the switching module is shown in Figure 2.
2 Software Design
The main task of this switch software design is to configure the registers of the VT6510B switching chip to enable it to perform basic switching functions. In addition, the host computer can configure this switch through the RS-232 port or the network port on the switch to realize various advanced management functions such as network port status monitoring, redundant loops, and virtual LAN.
Based on the product design requirements, the software of a switch can be divided into the following parts:
(1) Initialization
The main task is to set the initial values of each register in the CPU and the registers in the switching chip, and then start the switch to work.
(2) Network Protocol
It implements 802.1d, 802.1w, 802.1q, as well as network protocols such as PING, ARP, BOOTP, IP, TCP, and UDP.
(3) Network management and function settings
The RS-232 port allows for the setting and monitoring of some basic switch parameters. Additionally, based on the aforementioned network protocols, parameter settings and real-time status monitoring of the switch can also be performed directly over the network.
(4) Fault diagnosis and implementation of redundant loops
It enables self-diagnosis and alarm for faults in power supply and other components of the switch, implements protocols and policies according to the set redundant loops, monitors the current network connection status, and realizes the network's self-healing function.
Because industrial Ethernet switches share many similarities with, yet also differ from, commercial Ethernet switches were designed with the principles of commercial Ethernet switches in mind while also taking into account the specific characteristics of industrial Ethernet devices. This design utilizes powerful switching chips, network physical layer chips, and transceiver interface circuits, and employs a 32-bit embedded processor based on an ARM core to implement the switch's advanced network functions.
