Universal Robots Forum

Modbus signal with 0 update freq. and Output Action bug

When a Modbus TCP digital output is set to:

  • Update frequency of 0 (update on write), and
  • Output action: Low when not running

Then the signal is spammed to the recipient of the digital output in an uncontrolled manner when the program stops.

What I would expect from this configuration is that the value is only written once when the program stops and that’s it.

I’ve tested this on both a CB3 series robot with SW version 3.12 and one with 3.15.3 and both have this “feature”.

This behavior is quite undesirable because this overloads the recipient of all the requests.
It basically mimics a DDoS attack on the unit connected.
And the problem only gets bigger if multiple signals are added with output actions and freq 0 because the signals are sent as separate writes.