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
20-6
A5E00739858-01
20.3 Overview of the S7 Communication Blocks
Classification
For S7 communication, connection configuration is needed. The integrated
communication functions are called up with the SFBs/FBs or an SFC/FC from
within the application.
These blocks can be classified in the following categories:
SFBs/FBs for data exchange
SFBs for changing the operating status
SFBs for querying the operating status.
SFC/FC for querying the connection.
Availability of the S7-300/400 Communication Blocks
The blocks for the S7-400 are in "Standard Library".
The loadable blocks for the S7-300 are in the "SIMATIC_NET_CP" library.
To run the S7-300 blocks, you need a SIMATIC NET CP in the S7-300 series. For
further information, please see the related documentation.
SFBs/FBs for Data Exchange
Communication SFBs/FBs for data exchange are used to exchange data between
two communication partners. If an SFB exists only on the local module, this is
referred to as unilateral data exchange. If an SFB/FB exists on the local as well as
on the remote module, this is referred to as a bilateral data exchange.
Blocks
S7-400
Blocks
S7-300
Description Brief Description
SFB 8
SFB 9
FB-8
FB 9
USEND
URCV
Rapid unacknowledged exchange of data irrespective of
the sequential execution of the communication function
(URCV) at the communication partner (for example,
operational and maintenance messages). This means
that the data can be overwritten by more recent data at
the communication partner.
SFB 12
SFB 13
FB 12
FB 13
BSEND/
BRCV
Secure transfer of a data block to the communication
partner. This means that data transmission is not
completed until the receive function (BRCV) in the
communication partner has accepted the data.
SFB 14 FB-14 GET Program-controlled reading of variables without additional
communication function in the user program of the
communication partner.
SFB 15 FB 15 PUT Program-controlled writing of variables without additional
communication function in the user program of the
communication partner.
SFB 16 FB 16 PRINT Sending data to a printer (S7-400 only)