Modbus Local Serial Communication Interruption

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An interruption in Modbus local serial communication. This means the drive has lost communication with its Modbus master or other devices on the local serial network, preventing remote control, monitoring, or data exchange. This can lead to a loss of process control.

• Broken or disconnected RS-485 communication cable (e.g., twisted pair to terminals A+, B-).
• Incorrect Modbus communication parameters (e.g., baud rate, parity, slave address, P1-30, P1-31).
• Termination resistor (120 Ohm) missing or incorrectly placed on the Modbus network.
• Faulty Modbus master device or interference on the communication bus.

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1. 1

   1. Verify physical cable connections to the drive's RS-485 terminals (e.g., A+, B-, GND) for secure contact.

2. 2

   2. Check Modbus communication parameters in the drive (e.g., P1-30 for address, P1-31 for baud rate) and ensure they match the master.

3. 3

   3. Use a Modbus analyzer or oscilloscope to check signal integrity on the RS-485 bus at the drive terminals.

4. 4

   4. Confirm that termination resistors (120 Ohm) are correctly installed at both ends of the RS-485 bus.

5. 5

   5. Temporarily disconnect other devices from the Modbus network to isolate potential conflicts or noisy devices.