Master: Busoff Detection

Master Unit LED		Error	Description
MS	NS
Green Light ON	Red Light ON	Busoff detection	Communication stopped due to critical error.
		Duplicate MAC ID	The MAC ID configuration was duplicated. (This error occurs only during unit start-up)

Process Flowchart

* See also:

Symbol	See also:
1	Disconnected Terminating Resistors, Cable Disconnection, Disconnected Connector, and Disconnected Signal Wire
2	Loose Connector and Signal Wire
3	Noise Intrusion

Causes of Error

Possible Cause	Examination Method	Countermeasure
Disconnected terminating resistors Cable disconnection Disconnected connector Disconnected signal wire	Check that terminating resistors are connected to both ends of the network. Measure resistance between signal wires with communications power supply OFF. → Normal: 50 to 70 Ω Measuring point: Connection of the problem unit See also: Disconnected Terminating Resistors, Cable Disconnection, Disconnected Connector, and Disconnected Signal Wire	Fix the problem. How to find the trouble point: Remove the terminating resistor on one end of the network. The trouble point is where resistance changes from 120 Ω.
Loose connector Loose signal wire	Check for the connection of connectors and signal wires. The connectors and signal wires should be firmly connected. Checkpoint: all nodes and all branch taps See also: Loose Connector and Signal Wire	Connect the connectors and signal wires again.
• Voltage drop of communications power supply	Measure voltage of communications power supply at the unit with a trouble. → Normal: 11V or more between V+ and V− • If the voltage is 11 to 14 V, the unit is a possible cause. Fix the problem on the unit.	Check the voltage of the power supply. Calculate the current capacity of the cable and add more communications power supplies.
Noise (external cause)	Check the noise intrusion via the following paths (1) to (3). Noise via DRAIN (FG) Induced noise via communication cable Communications power supply → See also: Noise Intrusion	Take countermeasures against noise.
• Broken unit	Replace the trouble unit with a new one. → Verify whether the problem is fixed.	Replace the unit with a new one.
No cause is identified.	Identify the trouble point by dividing the network. → See also: Broken Unit Examination (Dividing Network Examination)