Modbus Communication Error

What does CE Memobus Com Err mean?

Control data was not received correctly for two seconds, indicating a breakdown in Modbus communication. This fault occurs when H5-05=1 and H5-04=0 to 2, typically due to a broken connection or the master stopping communication.

• Intermittent break or loose connection in the Modbus RS-485 cable due to vibration, mechanical stress, or poor terminal contact (DA+, DB-).
• Incorrect Modbus communication settings (e.g., baud rate in Parameter H5-04, drive address in H5-01) preventing proper data exchange.
• Master controller (e.g., PLC or HMI) failing to send valid Modbus queries or polling the drive too slowly, causing timeouts.
• Excessive common-mode noise on the RS-485 bus causing data corruption, especially in long cable runs without proper shielding.
• Faulty or missing termination resistors (e.g., 120 Ohm) at either end of the Modbus segment leading to signal reflections.

Click steps to track your progress.

1. 1

   Verify Modbus communication parameters: drive address (H5-01), baud rate (H5-04), and data format (H5-05) match the master controller's settings.

2. 2

   Inspect Modbus RTU (RS-485) wiring on terminals DA+, DB-, and GND for secure connections, proper shielding, and continuity using a multimeter.

3. 3

   Measure the differential voltage between DA+ and DB- terminals on the Modbus network during communication attempts to confirm proper signaling (e.g., -5V to +5V range).

4. 4

   Check for correct termination resistors (e.g., 120 Ohms) at both physical ends of the RS-485 segment, measuring resistance across the terminals.

5. 5

   Use a Modbus diagnostic tool or protocol analyzer to monitor frames and identify corrupted packets or a lack of communication from the master.