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4. Troubleshooting (DeviceNet)
4.1.3 Procedures for Examining Possible Causes
4.1.3.1 Connection Problem (Disconnected Terminating Resistors, Cable
Disconnection, Disconnected Connector, Disconnected Signal Wire)
(1) Ensure that two terminating resistors are connected to both ends of the network.
(2) Turn OFF the communications power supply.
(3) Measure resistance between CAN_H and CAN_L wires of the absent slave using the
tester.
Tes ter
Measure resistance between signal wires with tester.
Ω
Blue (CAN L)Red (CAN H)
Resistance Determination
0 Ω Shot circuit
Under 50 Ω Three or more terminating resistors on one network
50 to 70 Ω Normal
70 to 120 Ω Error (cable disconnection or disconnected signal wire on the
trunk line)
Over 120 Ω Error (cable disconnection or disconnected signal wire on drop
line or trunk line → Both CAN_H and CAN_L)
(4) How to find the trouble point:
- Remove the terminating resistor on one end of the network.
(The resistance at the point where the terminating resistor is connected is 120
Ω.)
- Measure resistance at branch taps of all units.
- The trouble point is where resistance changes from 120 Ω.
- After finding the trouble point, verify the connector and cable conditions.
98 Fieldbus I/O Rev.6