CAN Error Types : Bit, Stuff, CRC, ACK & Form Errors

Introduction: Error detection and management are fundamental to CAN’s reliability. The CAN protocol defines several distinct error types such as bit errors, stuff errors, CRC errors, ACK errors and form errors. Each of these error types indicate a specific violation or failure during message transmission or reception.

Bit Error

• The bit error occurs when the bit value a node is transmitting does not match the bit value it simultaneously reads back from the bus.
• When it is detected: During transmission (by the transmitter only).

Stuff Error

• The Stuff Error occurs when the “bit stuffing” rule is violated. The rule states that after five consecutive bits of the same polarity (five 0s or five 1s), the transmitter must insert a “stuff bit” of the opposite polarity.
• When it is detected: During reception of a message (by any node)

CRC Error

• The CRC Error occurs when the CRC value calculated by a receiver does not match the CRC value included in the frame by the transmitter.
• When it is detected: After the Data Field and before the ACK slot (by receivers).

ACK Error

• This error indicates that a transmitted message was not received by any other node on the network. An ACK Error occurs when the transmitter does not detect a dominant bit in the “Acknowledge” (ACK) slot of the frame it sent.
• When it is detected: In the ACK slot of the frame (by the transmitter only).

Form Error

• This error occurs when a received frame violates the fixed structure of the CAN protocol. A Form Error is detected when one of the fixed format fields in a CAN frame contains one or more illegal bits.
• When it is detected: In specific, pre-defined recessive fields of a frame (by any node).

Summary: These error mechanisms ensure the integrity and correctness of messages and help maintain the stability of the network even under noisy or fault prone conditions. It helps in building reliable, fault tolerant CAN based systems in automotive or industrial applications.