MEMOBUS Communication Error

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This fault occurs when communication via MODBUS (MEMOBUS) is interrupted for longer than 2 seconds after initial communication has been established. This indicates a loss of data exchange with the control system or HMI, which can lead to uncontrolled operation, system downtime, or failure to receive critical commands.

• Damaged or improperly connected RS-485 communication cable (e.g., A/B lines reversed or open circuit).
• Incorrect MODBUS parameters (e.g., P5-01 Baud rate, P5-02 Data bits/Parity, P5-03 Station address) configured in the inverter or master device.
• Missing or incorrect termination resistor on the MODBUS network (e.g., 120 ohm resistor across A and B lines).
• Excessive electrical noise or ground loops on the communication bus interfering with data integrity.
• Overloaded MODBUS network with too many devices or excessive cable length beyond specifications.

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1. 1

   Inspect RS-485 cable connections at inverter terminals S+, S- and the master controller, ensuring correct polarity (A to A, B to B).

2. 2

   Verify MODBUS parameters P5-01 (Baud rate), P5-02 (Data bits/Parity), and P5-03 (Station address) match between inverter and master.

3. 3

   Measure the voltage across RS-485 terminals S+ and S- (typically differential 0.2V to 5V during communication) using an oscilloscope.

4. 4

   Confirm the presence and correct placement of 120-ohm termination resistors at both ends of the RS-485 bus.

5. 5

   Test communication with a single known good MODBUS master directly connected to the inverter to isolate network issues.