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hmi master on the bus

11/20/2015 10:28 AM	Rate (0)
Ziemens Gold Member Joined: 3/2/2007 Last visit: 1/9/2026 Posts: 999 Rating: (5)	we have 4 wincc flexible hmi's with one s7400 plc on our machine . should each hmi's connection settings be "Only master on the bus" checked ? or not ? also how much should we put the Network "Number of masters" ?
	Last edited by: Ziemens at: 11/20/2015 10:31:18 AM ... thank you ...
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11/20/2015 10:47 AM	Rate (0)
Wizard Diamond Expert Joined: 4/24/2006 Last visit: 1/9/2026 Posts: 9104 Rating: (1202)	Hello Ziemens, Perhaps the following threads might help: 3 Siemens HMI on same Profibus DP. Should all of them be 'only master on the bus'?!? https://support.industry.siemens.com/tf/ww/en/posts/23443/ Best regards, Wizard

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11/20/2015 11:27 AM	Rate (0)
Ziemens Gold Member Joined: 3/2/2007 Last visit: 1/9/2026 Posts: 999 Rating: (5)	what does it actually mean "Only master on the bus" for an hmi ?
	... thank you ...
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11/20/2015 11:45 AM	Rate (0)
Wizard Diamond Expert Joined: 4/24/2006 Last visit: 1/9/2026 Posts: 9104 Rating: (1202)	Hello Ziemens, Please have a look at the following thread: https://support.industry.siemens.com/tf/ww/en/posts/89281/ (See the answer of Dchartier) A HMI panel is a Profibus Class 2 master. Best regards, Wizard

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11/26/2015 3:51 PM	Rate (0)
Ziemens Gold Member Joined: 3/2/2007 Last visit: 1/9/2026 Posts: 999 Rating: (5)	If you do NOT set the "Only master on bus", a device that is master will check the bus settings before attempting to connect to the bus. If there is then already a master, and this master uses different bus settings, the connection attempt is stopped. If you DO set the "Only master on bus", the device that is master will NOT check the bus settings before attempting to connect to the bus. If there is then already a master, and this master uses different bus settings, the new master will try to connect, possibly causing a bus failure for the other master. In other words, I see no reason to select the "Only master on bus". Only advantage would be that the connection would be slighly faster, at the risk of causing bus failures.
	... thank you ...
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