Modbus multidrop network


Thread Starter


How can I implement a Modbus multidrop network ? What kind of modems do I need ? How is the actual wiring done ? and has anybody installed a modbus multidrop network with the Foxboro Integrator 30 communications module as the master node ?

Rob Entzinger Schneider Automation

MODBUS is a protocol.

It can communicate on any layer0. RS232, RS485, Radio etc. Master/Slave

MODBUSPLUS is the same protocol on an ASIC chipset the is a peer to peer

Rob E.
Here some links and tips.
First you can find the Modicon modbus protocol reference guide at<>
Type of modems and how to do your wiring: Take a look at
<> and at
We used the modbus simulator software from Calta Computer Systems <> (you can download a thirty day trial
version) for testing our master and slave modules separately.
Douglas, why don't you post this message at the foxboro mailinglist?
Jan Stas

Yonca Yesilipek

For Foxboro side you should define Integrator 30 as MOD30 in your system
definiton. MOD30 works as a Modbus RTU Master with two RS232 ports. In order to implement modbus Multidrop networks, other devices should be configured as Modbus RTU slave and should be connected with daisy chain ( most probably they support RS485), slave adresses should be defined also. If your devices uses RS485, you should use RS232/485 converter on Foxboro side.

MDSCAN block should be created for each device on bus in MOD30. This block scans
the RTU slaves and establishes the communication. You can see the status of
communication on System Management screen of Foxboro.
If you need any more information, let me know.
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