CAN Bus Termination Resistor: Complete Technical Guide
Learn why CAN bus termination resistors are critical, how to calculate correct values, and best practices for signal integrity.
Why CAN Bus Termination Matters
The CAN bus is a differential signal transmission system where data travels along two wires (CAN H and CAN L) as voltage differences. Without proper termination, signal reflections occur at the end of the bus cables, causing data corruption and communication failures.
Termination resistors match the characteristic impedance of the CAN bus cables, effectively absorbing reflected signals and preventing them from bouncing back down the line. This is fundamental to reliable CAN network operation.
Standard CAN Termination: 120Ω Resistors
The Standard Rule
Standard CAN bus networks use 120Ω termination resistors connected between CAN H and CAN L at each end of the network. This value is specified in the CAN standard (ISO 11898-2) and is essential for proper operation.
CAN H ──[120Ω]──┬──── (Bus End)
│
CAN L ──────────┴──── (Bus End)
Identifying Termination Problems
Symptoms of Missing Termination:
- Intermittent communication failures
- Increased CRC errors on the CAN bus
- Messages arriving with corrupted data
- Device arbitration failures
- Behavior improves when devices are close together
Symptoms of Incorrect Termination:
- Wrong resistor values (not 120Ω)
- Too many termination points
- Terminators in wrong locations (middle of bus)
- Results in impedance mismatch and signal degradation
Best Practices
Place terminators physically at the last node on each end of the CAN bus trunk.
120Ω, 1/4W, 5% tolerance, metal film or carbon film construction
Should be approximately 2.5V each. Deviation indicates termination problems.
Automotive applications require resistors rated for -40°C to +125°C range
Debug CAN Bus Issues with RCAN Viewer
RCAN Viewer helps identify CAN bus problems including termination issues by analyzing signal quality, error rates, and message patterns in real-time.
Download RCAN Viewer