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Asked:18 Oct 2025

SIMATIC WinCC flexible: Smartaccess Authorization key Key Transmit Towards an Multi panel 370

Hi All,
I have two MP370 15" touchscreens, one each on seperate machines. Using the automation license manager, I was able to transfer one license key for SmartAccess over to the first HMI no problem once the type of comms, addressand device were selected, I'm communicating via MPI/DP. When I connect my PG Unit to thesecond machine I'm unable to detect the HMI even though I can see its nodeactive on the Simatic Manager.
There is one difference between the HMI comms setup in WinCC flexible and that is for the HMI with the successful download, the check box for "only master on the bus" has been ticked where as the other is not ticked so will thisstop mefrom being able to link up? Unable to exit runtime at the moment to check any settings in its control panel, is there anything to look for in the HMI's control panel that will stop me from communicating between the PG Unit and the HMI?
Thanks for any help,
Adrian

#sosflex #SIMATIC WinCC flexible #siemens
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Answers(1)
Siemens Test Added an Answer on18 Oct 2025

Troubleshooting Communication with MP370 HMI

Dear Adrian,

The "only master on the bus" setting is likely the cause of your communication issue. When enabled, the HMI will actively reject communication attempts from any device not configured as a master, potentially blocking your PG unit.

Here's a breakdown and troubleshooting steps:

  1. Disable "Only Master on the Bus": Ideally, you should disable the "only master on the bus" option in the HMI's communication settings. However, you mentioned being unable to exit runtime.
  2. Force HMI to Stop Runtime (if possible): Attempt a hardware reset of the HMI (check the MP370 manual for the correct procedure). This might force it out of runtime, allowing you to access the control panel.
  3. Check HMI Control Panel (if accessible): If you can access the control panel, navigate to Communication Settings -> MPI/DP. Verify the configured master stations and ensure your PG/PC interface is not blocked.
  4. ALM License Transfer Check: Double-check in the Automation License Manager (ALM) that the license is properly unlocked and associated with the correct hardware ID of the second HMI.

For detailed information on MP370 communication and the "only master on the bus" setting, please refer to the following SiePortal resources:

If the issue persists, consider collecting a project backup (if possible) and opening a support request via Siemens Support.

Sincerely,

Siemens Self Support

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