I know that I am fascinated by everything related to electronics, but from any point of view, today's field-programmable gate arrays (FPGAs) are all "outstanding" and really great devices. If in this era of intelligence, in this field, you want to have a skill, you have not paid attention to FPGA, then the world will abandon you, the era will abandon you. Author ALIFPGA, many years of FPGA development experience, all articles are a summary of years of study and work experience.
CAN bus is a serial data communication protocol. Its communication interface integrates the physical layer and data link layer functions of CAN protocol, which can complete the framing processing of communication data, including bit filling, data block coding, and cyclic redundancy. Inspection, priority discrimination, etc.
CAN bus structure
The CAN bus specification uses a three-layer network structure of ISO-OSI (Open System Interconnection Reference Model), and three different devices correspond to it.
Corresponding to the physical layer is the transceiver;
Corresponding to the data link layer is the CAN controller;
The application layer is mainly a user-specific application, and the corresponding device is a microcontroller.
CAN bus standard frame
Standard frame 11-bit identifier.
Frame type Data frame, remote frame, error frame, and overload frame
Data frame: The data frame carries data from the transmitter to the receiver. Most of the frames transmitted on the bus are this frame.
Remote Frame: Issued by the bus unit to request the transmission of a data frame with the same identifier. Data frames (or remote frames) are separated from each other by interframe space.
Error frame: An error frame is issued on any unit but a bus error is detected.
Overload Frame: An overload frame is used to provide an additional delay between the preceding and subsequent data frames (or remote frames).
The frame begins with a start frame (SOF) bit, and SOF is dominant, allowing hard synchronization of all nodes. The SOF is followed by an arbitration field consisting of 12 bits, each with 11 flag bits and a Remote Transmission Request (RTR) bit. The RTR bit is used to distinguish that the message is a data frame.
(RTR bit is dominant) or remote frame (RTR bit is recessive).
The arbitration field is followed by a control field consisting of 6 bits. The first bit of the control field is the Identifier Extension (IDE) bit, which should be a dominant state to specify a standard frame. The next bit of the extension bit is identified as a zero reserved bit (RB0), which is defined by the CAN protocol as a dominant bit. control
The remaining 4 bits of the field are Data Length Code (DLC), which is used to specify the number of data bytes (0 to 8 bytes) contained in the message.
The control field is followed by a data field containing any data bytes to be sent. The data field length is defined by the above DLC (0 to 8 bytes).
The data field is followed by a Cyclic Redundancy Check (CRC) field to detect packet transmission errors. The CRC field contains a 15-bit CRC sequence followed by a recessive CRC delimiter.
The last field is the acknowledgment field (ACK), which consists of 2 bits. During the execution of the acknowledgment slot (ACK Slot) bit, the transmitting node issues a recessive bit. Any node that receives an error-free frame will send back a dominant bit (regardless of whether the node is configured to accept the message or not) to confirm that the frame was received correctly. The confirmation field ends with a recessive confirmation delimiter, which may not be allowed to be rewritten as a dominant bit.
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