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Welcome to the CAN-on-DSP-TMS320F28335 wiki!
A data transmission protocol is defined to make sure the data transfer accurate and fast.
The whole protocol consist of three layer, as shown in the figure:
The main advantage of CAN over alternative networks is the high reliability. CAN controller and interface cost are as low as legacy data transmission products and are available off-the-shelf from leading semiconductor manufacturers.
The Data-Link Layer is responsible for transferring messages from a node to the network without errors. It handles bit stuffing and checksums, and after sending a message, waits for acknowledgment from the receivers.
The Physical Layer is the basic hardware required for a CAN network, i.e. the ISO 11898 electrical specifications. It converts 1’s and 0’s into electrical pulses leaving a node, then back again for a CAN message entering a node. Although the other layers may be implemented in software or in hardware as a chip function, the Physical Layer is always implemented in hardware.
In the CAN bus architecture, the Application Layer provides the upper-level communication functions of the OSI layered model. These functions have been implemented and will be introduced in chapter Application Layer.
Since CAN is a broadcast system, a transmitting node places data on the network for all nodes to access. As shown in CAN bus data flow , only those nodes requiring updated data allow the message to pass through a filter that is set by the network designer – i.e., messages from certain nodes can pass, and all others are ignored. If this filter is not used by a system designer, much of a node's µC processing time is spent sorting through messages that are not needed.
The High-Speed ISO 11898 Standard specifications are given for a maximum signaling rate of 1 Mbps with a bus length of 40 m and a maximum of 30 nodes. It also recommends a maximum un-terminated stub length of 0.3 m. The cable is specified to be a shielded or unshielded twisted-pair with a 120-Ω characteristic impedance (ZO). The Standard defines a single line of twisted-pair cable with the network topology as shown in this figure. It is terminated at both ends with 120-Ω resistors, which match the characteristic impedance of the line to prevent signal reflections. According to ISO 11898, placing RL on a node should be avoided since the bus lines lose termination if the node is disconnected from the bus.