Research and analysis on the data exchange between can and Ethernet

1. Technical background

The Can (controllerareanetwork--controller LAN) is a high performance serial data local communication network composed of can controller, and is one of the most widely used fieldbus in the world. It was first introduced by Bosch, Germany, and used for data communication between internal measurement and execution parts of automobiles. Its bus specification has been established as an international standard by ISO estimation standards Organization. It is considered as one of the most promising fieldbus because of its many advantages, such as multi-host, long transmission distance (10km), fast transmission speed (1Mbps) and strong anti-interference ability.

The can protocol is based on the open System Interconnection model of international standard Organization. In September 1991, Philipssemiconductors developed and released the can technical specification Version2.0 as the current highest version. Two modes are defined: Standard mode and extended mode. This article mainly introduces the standard mode.

TCP/IP (transmissioncontrolprotocol/internetprotocol--Transmission Protocol/Network Protocol) is an industrial standard protocol set, including IP, TCP, UDP and other protocols to ensure the correct transmission of data on the network. TCP/IP protocol is the foundation of modern Internet.

The TCP/IP protocol is a four-layer model: Application layer, Transport layer, network layer and data link layer. Each layer has a different function, and the layers and layers are logically independent of each other. Each layer corresponds to a number of sub protocols, as shown in Figure 1. The protocols used in this article include ARP, IP, and TCP.

2. Application background

Can bus is widely used in many industries. The local area network composed of it can connect a lot of bottom measure and control equipment, the farthest distance can reach 10km (under the condition of not receiving the repeater). Compared to other fieldbus, the distance is already very far. But with the development of Ethernet, people want to be able to carry on the real sense remote control to the bottom device too. IPC Plus interface card has been used to achieve this goal, but the price and interface card bottlenecks caused by the problem also exposed. This paper is based on SCM, can device and network chip as the core module to complete the function of the description. This approach lowers costs and avoids bottlenecks.

3. Hardware part

There are a variety of hardware implementation, can use integrated TCP/IP protocol MCU plus can transceiver and controller, can also use integrated can controller MCU plus can transceiver and network chip. The example of this paper adopts philipsp89c668 with no integration, plus can controller SJA1000, can transceiver TJA1050 and network chip rtl8019as to form a conversion module, the function module is shown in Figure 2.

p89c668: Microcontroller, the main control part, realizes the control to the network chip and can device, and carries on the protocol conversion between the two.

Sja1000:can Controller, two modes of operation (Basiccan and Pelican). Basiccan only supports standard mode, Pelican supports CAN2.0B standard and extended modes (this article only describes Basiccan mode). The error analysis function is supported and the can transceiver is controlled, which provides a simple interface for the microcontroller to control the can bus.

Tja1050:can transceiver, micro-controller to the can controller for the corresponding configuration, the transceiver automatically completed the corresponding can bus action.

RTL8019: The network chip, provides to the microcontroller to control the Ethernet the simple interface, causes the microcontroller only to be able to read and write to it to complete the operation to the Ethernet.

In addition, a can module is used as a can node in the experiment, and a simple can network is formed together with the conversion module.