2 Nos master polling data from slave in Modbus-RTU


Thread Starter

Anand Singh

2 Nos. RS-485 ,Nodbus-RTU communication port from drives,

1.one (FO redundant) to DCS

2.one No( Cu/FO redundant) for data concentrator

As there will be 2 master to poll the slave ,Communication is possible in this case from 2 masters which shall collect data from VFD
Repetaer used in VFD panel is :Universal RS 485 Fiberoptic Repeater
OZD 485 G12(-1300) PRO.

Is this possible ?
Any addtional hardware is required for this purpose ?

Jerry Miille

I do not fully understand your application but we offer a product that allows 2 (or 3) Modbus Masters to successfully communicate with a network of one or more Modbus Slaves. See this data sheet


Is this what you are looking for?

If you have any questions, please contact us at the addresses on the data sheet.


Jerry Miille

Patrick Lansdorf

Dear Anand,

Normally one would need some sort of synchronization between the two masters, so that only one master at a time will communicate with the slave, otherwise there will be collisions on RS485.

Personally, I would probably solve it the following way:
Set up one master as master over the Slave and add a Modbus slave to Modbus slave gateway, such as:
http://www.anybus.com/support/support.asp?PID=234&ProdType=Anybus X-gateway

The above master will poll the slave and write that data to the gateway. The gateway will copy the data to its second Modbus interface, which will be polled by the second master.

Just my 2 cents

Patrick Lansdorf