CAN, which stands for Controller Area Network, was developed by the German company Bosch, renowned for its expertise in automotive electronics. It eventually became an international standard (ISO 11898) and is one of the most widely used fieldbus systems globally. Initially designed for in-vehicle communication, CAN bus offers high-speed data transmission, exceptional reliability, and flexibility. In the 1990s, it gained popularity in the automotive industry and became the preferred communication protocol. Beyond vehicles, it has found extensive use in medical devices, industrial automation, building systems, and transportation.
CAN bus includes a robust error detection mechanism, defining five types of errors to ensure reliable data transmission. These errors are:
1. **Bit Error**: Nodes monitor the bus while transmitting. If the transmitted bit does not match the monitored level during the arbitration phase, a bit error is detected. However, if this mismatch occurs during the ACK segment or passive error flag, it is not considered a bit error.
2. **Stuff Error**: During data transmission, if five consecutive identical bits are detected, a stuffing bit is inserted. If six identical bits are detected, a stuffing error is flagged.
3. **CRC Error**: Each data frame includes a CRC check. The receiver calculates the CRC and compares it with the received value. If they do not match, a CRC error is reported.
4. **Form Error**: An illegal bit in a fixed format field, such as a dominant bit in a position that should be recessive, triggers a form error.
5. **Acknowledgment Error**: After sending a message, the transmitter expects a dominant bit from the receiver in the acknowledgment field. If the receiver fails to respond, an acknowledgment error occurs.
When an error is detected, the node sends an error frame and increments its error counter. Each node has two counters: one for received errors and one for transmitted errors. If the counter is below 127, the node is active. Between 127 and 255, it is passive. Once it exceeds 255, the node goes offline and stops participating in communication.
Error flags are sent when an error is detected. Active nodes send an active error flag, while passive nodes send a passive one. If a CRC error is detected, the error flag starts after the ACK delimiter unless another error flag is already being sent. This system ensures that errors are quickly identified and addressed, maintaining the integrity of the network.
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