Siemens S7-300 appendix Establishing a connection for communication, Data exchange, Disconnecting

Communication 3.2 Communication services

Establishing a connection for communication

FB 65 "TCON" establishes communication between the CPU and a communication partner. You can establish up to eight connections. The CPU automatically monitors and holds the active connection.

Communication partner A must initiate the connection. When the connection of communication partner A is active, it transmits a request to connect to communication partner B. Communication partner B waits until it receives the request for a passive connection.

In your connection configuration, you define which communication partner activates the connection, and which communication partners respond to the request with a passive connection.

Both communication partners must have established their connection in order to be able to exchange data.

Data exchange

Bidirectional data exchange is enabled after you established communication, that is, data can be transmitted and received in parallel. FBs available for data exchange:

Name of the FB		Description
FB 63	"TSEND"	Transmit data
FB 64	"TRCV"	Receive data

You can transmit and receive up to 1460 bytes of user data.

Disconnecting

FB 66 "TDISCON" disconnects the CPU from a communication partner.

Communication interruptions

Events causing interruptions of communication:

•You program the cancellation of connections at FB 66 "TDISCON."

•The CPU goes from RUN to STOP.

•At POWER OFF / POWER ON

Reference

For detailed information on the blocks described earlier, refer to the STEP 7 Online Help.

CPU 31xC and CPU 31x, Technical data	3-25
Manual, Edition 08/2004, A5E00105475-05