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Why Does the A6 Driver Occasionally Fail to Respond to RS485 Commands?

C

Chloe Jin

Last updated on Oct 23, 2026

Symptom

You may experience intermittent communication timeouts with the A6 driver. Specifically, communication may be stable when the drive is powered on but disabled. However, once the drive is enabled, you may encounter a timeout on approximately 1 in 10 or 1 in 20 messages. Resending the command usually resolves the issue.

Cause Analysis

This behavior is a common phenomenon in industrial communication known as Electromagnetic Interference (EMI).

  1. Physical Connection: Since the driver responds correctly when disabled, physical wiring and basic communication connections are likely correct.

  2. Hardware Health: Since the motor and driver operate normally otherwise, the hardware itself is not defective.

  3. The Trigger: The issue appears specifically when the servo enable is activated.

When the drive is enabled, the internal power circuits switch at high speeds, generating strong electromagnetic noise (EMC). This noise can couple into the RS485 communication lines, contaminating the signal and causing data packet corruption or loss, which results in communication timeouts. If you are using a USB-to-RS485 converter, which typically has lower noise immunity, the system is more susceptible to this interference.

Solutions

To resolve this issue, please check the following items in order of priority:

1. Check Grounding and Cable Shielding (Most Likely Cause)

  • Ensure the driver is properly grounded.

  • Use a twisted-pair shielded RS485 communication cable (such as a shielded network cable) to minimize noise pickup.

2. Use Terminal Resistors

  • Connect a terminal resistor to the RS485 output port of the last driver in the communication chain. This helps prevent signal reflections that can corrupt data.

3. Connect Grounds (GND)

  • Connect the GND pin of your RS485 converter (or USB-to-RS485 adapter) to the GND pin of the A6 driver.

  • This establishes a common reference potential for all RS485 devices, which effectively reduces common-mode interference.

4. Lower the Communication Baud Rate

  • A lower baud rate is more tolerant of interference.

  • You can adjust the RS485 baud rate (Parameter C0A.09) via the A6 driver panel buttons or debugging software.

  • Try lowering the rate from the default (e.g., 115200 bps) to 38400 bps or 9600 bps to see if stability improves.

5. Add Ferrite Beads to Motor Power Lines

  • Wrap a ferrite bead (magnetic ring) around the motor power lines (U, V, W).

  • Important: Do not pass the ground wire through the ferrite bead. Only the three phase wires should go through the ring.

Summary

The core issue is electromagnetic interference introduced when the drive is enabled. The most effective first steps are to verify grounding and cable shielding, followed by ensuring proper terminal resistor configuration and GND connections between the converter and the driver.