Technical data

Table Of Contents
Overview over the S7 Communication and the S7 Basic Communication
System Software for S7-300/400 System and Standard Functions - Volume 2/2
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20.4 Overview of the Blocks for the S7 Basic
Communication
Classification of the SFCs for the S7 Basic Communication
Connection configuration is not required for the S7 basic communication. The
integrated communication functions are called via SFCs in the user program.
The SFCs are divided into two classes:
SFCs for exchanging data between an S7 CPU and other modules with
communication functionality, if the communication partners belong to the same
S7 station (identified by the preceding "I” for internal).
SFCs for exchanging data between an S7 CPU and other modules with
communication functionality, if the communication partners are connected to a
common MPI subnet (identified by the preceding "X” for external).
Communication with stations in other subnets is not possible with the SFCs for
S7 basic communication.
The SFCs for basic communication can be run on all CPUs of the S7-300 and
S7-400. With these CPUs, you can also write variables to the CPUs of the S7-200
and read variables from them.
SFCs for External Communication
Block Brief Description
SFC 65/
SFC 66
X_SEND/
X_RCV
Secure transfer of a data block to a communication partner. This means
that data transmission is not completed until the receive function
(X_RCV) in the communication partner has accepted the data.
SFC 67 X_GET Reading a variable of a communication partner without your having to
place a corresponding SFC on the communication partner. This
functionality is implemented in the communication partner of the
operating system.
SFC 68 X_PUT Writing a variable into a communication partner without your having to
place a corresponding SFC on the communication partner. This
functionality is implemented in the communication partner of the
operating system.
SFC 69 X_ABORT Aborting of an existing connection without data being transferred. The
corresponding connection resources are thus released again on both
ends.