It is possible to communicate two intelligent Slaves and you do this by configuring Direct Data excahnge from within you Hardware configuration.
I would suggest u use the Master PLC to collect all the Data from the Slave PLC's and communicate this to the HMI from the Master.
Rheinhardt
from Siemens Help File
Configuring Direct Data Exchange between PROFIBUS-DP Nodes
Introduction
In a configuration for direct data exchange (lateral communication), local input address areas of an intelligent DP slave or of a DP master are assigned to the input address areas of a PROFIBUS-DP partner.
The intelligent DP slave or the DP master uses these assigned input address areas to receive the input data that the PROFIBUS-DP partner sends to its DP master.
Number of PROFIBUS-DP Partner That Can Be Connected
The type of interface limits the total number of PROFIBUS-DP partners that are connected directly to a DP interface or are addressed over this interface by means of direct data exchange. A maximum of 32 PROFIBUS-DP partners can be addressed on the MPI/DP interface.
Applications
The following applications are possible for direct data exchange:
Starting Configuration
- Double-click the DP interface of the configured receiver (DP master or already configured I slave).
Select the "Configuration" tab.
To create new line in order to configure direct data exchange, click the "New" button.
- In the dialog that appears, select "DX" mode and assign the input address areas to each other (you can find more information in the online help for this dialog).
- Mode: "DX" for direct data exchange, ("MS" for master-slave)
Partner DP Addr.: PROFIBUS address of the DP partner
Partner Addr.: Address of the logically assigned address area (sender)
- Local Addr.: Address of the logically assigned address area (receiver)
