Why the lower CAN identifier wins
Watch two standard data frames arbitrate without treating every differing bit as an error.
Dominant and recessive
CAN uses dominant 0 and recessive 1. When a transmitter sends recessive but samples dominant during arbitration, it loses arbitration and becomes a receiver. This is normal bus sharing, not a transmission error.
Identifier comparison
For two standard data frames starting together, identifier bits are transmitted most significant first. The first differing identifier bit decides priority. A lower numeric identifier wins this comparison. Mixed frame formats and remote/data arbitration require the other arbitration fields too.
Priority is not fairness
Higher-priority traffic can delay lower-priority frames. A message's response time includes contention, blocking and retransmissions. Average bus load alone cannot establish a worst-case deadline.
Arbitration, step by step
0010010000000100101000Both send their 11-bit identifiers most significant bit first.
Both start
Nodes observe an idle bus and begin together.
Conceptual sequence. Timing is slowed for learning; it is not a hardware measurement.
Your investigation
0x120 and 0x128 standard data frames start together. Find the first differing identifier bit and identify the winner.
Reveal the investigation checklist
- Write both 11-bit identifiers.
- Compare from most significant bit.
- Find the first 0-versus-1 difference.
- Explain why the losing node does not report a bit error for arbitration loss.
A node sends recessive and observes dominant during identifier arbitration. What happens?
Answer the knowledge check correctly to complete this lesson.
Think through Why the lower CAN identifier wins
Ask for an explanation, an automotive example or a question that tests your understanding.
Checking mentor availability…