The family based on can bus controller design and implementation (1)

Introduction

CAN (Controller Area Network) bus is Germany Bosch company to solve many of the modern automobile control and test equipment of data exchange and the development of a serial data communications protocol, it is a lot of main bus, communication medium can be twisted pair and coaxial cable or optical fiber, communication speed up to 1Mbps, communication distance of up to 10km, CAN Protocol one of the greatest features is to abolish the traditional station address coding, and replace it with the data block for the communication, the network for encoding the node number in theory is not restricted.

Due to the CAN bus with strong error correction capabilities, support for differential transceiver, and therefore suitable for high-interference environments, and has a long transmission distance. Thus, the can Protocol for distributed measurement and control in many areas is very attractive. At present CAN become standard, its characteristic ISO11898 as follows:

(1) CAN be an effective support for distributed control and real-time control of serial communication network.

(2) CAN protocols follow ISO/OSI model, use of the physical layer and data link layer and application layer.

(3) how CAN be multihomed, in essence, is also a CSMA/CD method, any one of the nodes on the network can be active at any moment to the other nodes on the network to send information, regardless of master-slave, a priority of between nodes, so communication is flexible; CAN use non-destructive bit arbitration technology, priority send, you can significantly save conflict and promoting the Conference time bus, in heavy load demonstrated good performance; CAN be point-to-point, point-to-multipoint (Group) and global broadcast several ways to transfer and receive data.

(4) CAN direct communication distances up to 10km (transmission speed to 5 Kbps); the highest communication speed up to 1Mbps (transmission distance of 40m).

(5) CAN the actual data of the node up to 110.

(6) CAN the data link layer used a short frame structure, each frame is 8 bytes, easy-to-error correction; each frame information CAN have a CRC error-checking, and other effective in minimizing data error rates; CAN nodes in error in serious cases, with automatic shutdown function, so that other nodes on the bus is not affected.

(7) signal modulation and demodulation mode uses the NRZ encoding/decoding, and insert the padding bits (bit stuffing) technology.

(8) bit has dominated the "0" (the Dominant bit) and concession "1" (Recessive bit) two logical values, use of clock synchronous technology, with hardware from synchronization and time tracking features.

The family based on can bus controller bus design programme

On entering the information age today, people living in safety, comfort requirements have increased, the establishment of residential computer management LAN, implementation of the integrated management of the community network is imperative.

By covering the entire residential home controller and a central computer system, for the intelligent management of dwelling.

Figure 1 is based on CAN bus architecture diagram, system used support CAN standard bus network.

The central computer system (PC PC) via the CAN interface adapter cards and CAN bus connected, for data exchange. Through the twisted-pair cable to a central computer system and home controller (lower intelligent node) hook in a bus, constitute a low-level communication network. As a result of the CSMA/CD information transmission control technology that allows the nodes on the bus contention on the bus, so equality can constitute the main node has multiple redundant network architecture.

In the lower-level communication network, the central computer system and family controller has its own ID sign.

As a result of using the standard as a CAN network communication protocols, each node in the network of the same, so we can move into the central computer system virtual, but the host is the virtual home controller into the response from the host machine. The central computer system is responsible for the entire CAN bus monitoring management, system parameters (such as transmission rate and node address, etc.), data transmission, data requests, native status query, node status query, interrupt status query functions. System work process for the PC to the next node (home controller) to send a command, the lower nodes to identify and implement the appropriate command. At the lower nodes can also be used to exchange information as required.

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