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Multiple Master at one network
Jul 19, 2006 2:00 pm, by Ståle Hope, Servo Electronics
Subject : Networking
 from the Automation List dept.
Text :
I have a network where the master communicate with different slaves. I want to add a second master to the network to communicate with an exisiting slave that already communicates with the original master. This system using Modbus RTU at 2-wire RS485.
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Re: Multiple Master at one network
Jul 27, 2006 12:03 pm, by Jerry Miille
Our Multii-Port module is specifically designed to provide this capability.
Look here for a data sheet http://www.miille.com/din366-10p.pdf
It works with either Modbus or Allen-Bradley DF-1 protocol. It has support for 2-wire RS-485 communication. If you have questions look on our website (http://www.miille.com) for contact information and additional details.
Jerry Miille
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Re: Multiple Master at one network
Jul 21, 2006 12:43 pm, by Anonymous
I don't know which plc or dcs system are you using, but remember that exists MODBUS PLUS designed at this time to have PEER TO PEER communications, that means you can configure multiple master in your net.
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Re: Multiple Master at one network
Jul 20, 2006 8:29 am, by Dave
Modbus RTU is designed to support only a single master. A thread on this forum addressed the feasibility of multiple masters using either a 3rd party bus moderator (Anybus) or Modbus TCP.
http://www.control.com/1026209439/index_html#1026209533
An alternative is to have the current #1 master read from the slave and then write that data to the 2nd master, which you configure not as a master, but as a slave.
Dave
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Re: Multiple Master at one network
Jul 20, 2006 7:32 am, by Dweebyone
You can not have two masters of a Modbus network. End of story.
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Re: Multiple Master at one network
Jul 21, 2006 12:32 pm, by Lorne
You can use a port multiplexor such as the PLC09 Arbitrator from Calta (http://www.calta.com) to do this. We have used this configuration many times in the past.
Regards.
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