For the S7-200s you have to have the HMI be the master for WinCC to work.

To attach more than one PLC via MPI and to share data between the PLCs you need to setup a back channel communications protocol in your tag database on WinCC. By this I mean you need to run all communications between the PLCs through the HMI. To do this setup the tags you need to share in WinCC tag database on both PLCs. Then on the trigger PLC (where the data originates) make sure the tag has the SET VALUE event linked to the other tag on the CHANGE VALUE trigger. Then make sure you include the tag on an active screen, there is not much logic here but it is the only way that WinCC will ensure the data transfer on compile (if a tag is not used in compile then it is not included).

For example in my application where I have this setup:

Pressure originates in PLC 1
PLC 2 is the network PLC to communicate to other devices

In the HMI I have a tag for Pressure_PLC1 and Pressure_PLC2
Pressure_PLC1 is the original data so the HMI have an output display for Pressure_PLC1. In Pressure PLC1 under Events the SetValue trigger is enabled with Tag(Out)=Pressure_PLC2 and Value=Pressure_PLC1

When the Pressure changes in PLC1 the tag value changes and it writes the data to PLC 2. It is not elegant but it does work for what you were describing. In the TP177 you have 1000 tags to use so it can work if your communications are efficient.

This lets the HMI control both PLCs while transferring data between the two.

I hope this gives you some ideas.

Regards

Eric

Both PLCs need to be slaves when on the same network as the TP177. That makes the way it cycles through communications between the PLCs kind of tough so you have to frame your program around the limitations of the MPI structure from the TP177.

Having the tags trigger though the HMI will work, but it is not a conventional system, and it takes a good bit of extra work to do it. For lack of a better way to describe it...it makes your HMI program on WinCC a real pain in the butt.

erblaha

Both PLCs need to be slaves when on the same network as the TP177. That makes the way it cycles through communications between the PLCs kind of tough so you have to frame your program around the limitations of the MPI structure from the TP177.

Having the tags trigger though the HMI will work, but it is not a conventional system, and it takes a good bit of extra work to do it. For lack of a better way to describe it...it makes your HMI program on WinCC a real pain in the butt.