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Why does a PLC get displayed as a busy controller with a question mark in the Network Explorer.

Goals and Symptoms

Why does a PLC get displayed as a busy controller with a question mark in the 'Network Explorer'.

Facts and Changes

ProWorx 32 version 2.1

Causes and Fixes


Why does 'ProWORX 32' display a PLC on the 'Network Explorer' window as a 'BUSY CONTROLLER'
with a question mark.


The reason that the PLC is displayed as a busy controller with a question mark is because it is a device that is
unsupported by '.ProWORX 32'. The 'Network Explorer' finds controllers, bridges, bridge multiplexers, and
other devices that are attached to the network. 'ProWORX 32' displays the PLC's that are found by using the
information that is stored in the PLC memory and the exec firmware (address number, type, operating mode,
and status). Because it cannot recognize the exec firmware, it does not know what information to display and
shows a question mark.

An unsupported device could be:

  • A Qauntum 984 PLC that has been upgraded to support Unity.
  • A Quantum Unity Co-processor PLC.
  • A Premium PLC with a Modbus Plus network adapter card.
  • A PLC on the network that does not support the 984 ladder logic used by 'ProWorx 32'.

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