Configuring Virtual I/Os for S7 400 using S7 300


Thread Starter

John Bastian

We have an S7 PLC 400 and an S7 PLC 300, but have not yet purchased Distributed I/O modules. Meanwhile, we would like to connect the 2 PLCs (either by Profibus, TCP/IP, Industrial Ethernet or any other method), so the PLC 400 can access I and Q addresses mapped to memory addresses (or I/Q) on the PLC 300. Thus, the PLC 400 can function as it would after we install I/O modules at the right addresses, without changing any code (or as little as possible...). Is it possible to do so? If so, how? Do we need to install any additonal hardware? software? GSDs?


Dobrowolski, Jacek


If both of them have Profibus DP ports, then you can configure S7-300 as a DP I-Slave.. Put both stations in one project. Connect them to the same DP network. S7-400 configure as Master, S7-300 as Slave. Define IO image for S7-300. In S7-400 HWConfig add configured station of type CPU 31x and connect your S7-300 station to it. Map S7-300 data to S7-400.

Jacek Dobrowolski
It is quite simple to do it.

1) Make a project with two PLC 1x CPU400, 1x CPU300 and without any I/O cards.
2) In HW Editor configure CPU400 as Master on Profibus and CPU300 as Slave on Profibus (be sure you have both CPUs on one Profibus net).
3) For CPU300 configure in 'configuration' (X2 DP-> Properties-> Configuration) I/O which are for CPU400 required (be careful, you are configuring CPU300 as first and from its point of view are I of CPU400 O of CPU300).
4) For CPU400 configure one Slave station of CPU31x type (in Catalog under Profibus DP->Configured Stations).
5) Open this Slave station and connect it with your CPU300 (it is configured already).
6) When is the Slave station opened chose Configuration and configure the I/O addresses for CPU400 (they should be the same as addresses of your final I/O cards).
7) At it's all. It should work.

On the CPU300 you run the simulation program of your target system/machine/technology.
You can simplify things greatly by purchasing the Siemens PLC Sim software. Using this simulator software you don't even need any hardware to test your program, and it's easy to use.