Direct Communication; Principle Of Direct Data - Siemens SIMATIC S7-400 Reference Manual

Structure of a CPU 41x
1.12

Direct Communication

You can configure direct communication for PROFIBUS nodes as of STEP 7 V 5.x.
The CPU 41x can participate in direct communication as the sender or recipient.
"Direct Communication" represents a special type of communication relationship
between PROFIBUS DP nodes.
1.12.1

Principle of Direct Data

Direct communication is characterized by the fact that PROFIBUS DP nodes
"listen in" to find out which data a DP slave is sending back to its DP master.
By means of this mechanism the "eavesdropper" (recipient) can access changes to
the input data of remote DP slaves directly.
During configuration in STEP 7, you specify by means of the relevant I/O input
addresses the address area of the recipient to which the required data of the
sender are to be read.
A CPU 41x can be:
Sender
Recipient
1-64
as a DP slave
as a DP slave or a DP master or as a CPU that is not
integrated in a master system (see Figure 1-17).
Automation System S7-400 CPU Specifications
A5E00165965-01