Watchdog of XC330-T288-T does not stop motor

I’m using an XC-330-T288-T. It is connected to a 12V power supply and communication runs through a Dynamixel Communication Bridge (to convert between TTL and RS485) and a Waveshare to convert between RS485 and USB. The motor is on the newest firmware version (v51) according to the Dynamixel Wizard.

The error occurs both using the Dynamixel Wizard or the Dynamixel Workbench to control the motor.

If doing the same actions with the same settings on a XM540-W270-R, everything works as expected, which is:

  • Set the bus watchdog to a positive, nonzero value, e.g. 127
  • Switch to any control mode (we are using CurrentControl)
  • Turn on torque
  • Send a command → The motor starts turning
  • Disconnect the Waveshare USB<->RS485 converter from USB (but leave the power supply connected), effectively stopping any communication

Expected behavior: The motor stops spinning after the watchdog timeout (127 * 20ms).

Observed behavior: The motor keeps turning indefinitely.

When resuming communication and reading out the value of the watchdog register, the value of the register is -1, indicating that the watchdog actually was triggered. To send any further command, the register also has to be set to 0 to reset the watchdog. Until then, the motor keeps turning.

Doing exactly the same with the XM540, the motor stops turning as expected. Comparing outgoing packets and their responses, they seem to be exactly the same for both motors, indicating that the XC330 has the watchdog successfully set active and subsequently triggered by the loss of communication. Somehow the firmware doesn’t seem to stop the motor, though.

Has anyone else experienced this error or can reproduce it?

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I was able to reproduce this behavior with all models of 330 sized DYNAMIXEL servos. It looks like a firmware related bug, and I’ve reported it to our development team for resolution.

For now, you can use the Firmware Recovery function to roll back to an older version of the firmware without this bug.

Thank you for bringing this to our attention.

Hey Jonathon, thanks for the reply! Can you hint me a firmware version that I should try out?

Quick followup: I tested all firmware versions and, unfortunately, the watchdog doesn’t work on any of them.


I just confirmed that myself here at the office as well, and I apologize for the unavailability of the Bus Watchdog feature on these servos at this time.

I’ve added an addendum to the bug report related to this on for our development team, and I’ll be sure to update you once a fixed firmware version has been released.

Thank you.