[quote user="SM"]Can I use two CP441 in S7-400H for redundant Modbus network without writing any additional logic?In this condition can I put the same Modbus address for both CP441 or not?

Hi,

Thats not possible, the mayor problem is that the Modbus Master is most of the time one system, or they have two Modbus Master that only switched when the other is switched down.

Normally it is possible to make two different point-to-point Modbus Master-Slave communications whereby the Modbus Master is deciding which Slave will be called, when there is nothing asked to the other slave then the slave gives no answers. When there is going something wrong with the Master then the other Master is going to ask his slave.

It is also possible to get a Multidrop line with RS485 where both Masters (or only one) isreading/writing to both slaves the Registers and Coils, whereby the Slaves have different Slave addresses, the Master have to detect which communication is not working any more and have toread/write to the other slave.

Or both slaves getting all data and in the S7-41xH this is controled...