1MDU07205-YN rev. F
REF601 CEI
User’s manual
95
Possible faults in:
RS485
Are the termination resistors placed at the end of the line?•
Are 2 termination resistors placed at each bus segment?•
Is the line polarity correct? Are the lines by accident swapped?•
Is the maximum line length exceeded?•
Modbus Communication parameters
Is baud rate correctly adjusted?•
Are the parity and the stop bit correctly adjusted?•
Is the slave address correct?•
Are there two devices with the same address in the system? If yes, fi x it!•
Modbus master
Is the request to response timeout correct?•
Is the Modbus silent interval between two telegrams > 3.5 character times?•
Notice that the slave device will not give any response when it is addressed •
with a broadcast (slave address = 0).
Modbus slave
Has the device a unique Modbus address?•
Is the function code supported by the device?•
Has the request a valid address?•
Has the request a valid quantity of coils, inputs, and registers?•
Is the power supply turned on for the relay unit?•
7.6 Communication troubleshooting
Serial Communication
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