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Unity returns 'This isn't a valid PLC Address, or PLC is busy' when trying to connect with Modbus Plus using the TSXCUSBMBP adapter

Goals and Symptoms
Attempts to connect to a Unity PLC returns the error message 'This isn't a valid PLC Address, or PLC is busy' when
trying to connect with Modbus Plus using the 'TSXCUSBMBP Modbus Plus adapter'.

Facts and Change
TSXCUSBMBP Modbus Plus adapter

Causes and Fixes
Attempts to connect to a Unity PLC using the 'TSXCUSBMBP Modbus Plus adapter' from a laptop PC fails with the
error 'This isn't a valid PLC Address, or PLC is busy, or media is off.'.  If you try to connect to the same PLC from
a different PC using Modbus Plus, the connection is successful.

The issue could occur if there are multiple devices listed for the same 'TSXCUSBMBP Modbus Plus adapter' in the
'MBX Driver Configuration' window due to repeatedly disconnecting and reconnecting the  'TSXCUSBMBP Modbus
Plus adapter' to the PC.  On some PC's, disconnecting any USB device might result in Windows not properly deleting
the the device from the operating system.   When you plug the USB device back in, Windows will create a new instance.
(This is an Windows operating system related issue.  It is not a product issue).  If this occurs with the 'TSXCUSBMBP
Modbus Plus Adapter', it could cause a new MBX Device to get created with a new device number. Because Unity is
designed to only utilize MBX Device number 0, any attempts to connect to the PLC will fail.

As a quick test, to determine if this scenario is the cause of the problem, try to read the PLC using MBX Demo.  If the test
fails, use the following steps to resolve the issue.
  • Open the 'MBX Driver Configuration' window.
  • Delete all of the instances listed.
  • Unplug the USB cable for the TSXCUSBMBP adapter from the PC.
  • Reboot the PC.
  • Plug the USB cable for the TSXCUSBMBP adapter back into the the PC.
  • Retest.
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