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
A5E00739858-01
20-7
SFBs for Changing the Operating Status
With SFBs for changing the operating status, you can control the operating status
of a remote device.
Data exchange with the SFBs for changing the operating status is unilateral.
Block S7-400 Brief Description
SFB 19 START Trigger the RESTART of an S7/M7-300/400 or C7-300 CPU, if it is in the
STOP operating mode.
SFB 20 STOP STOP of an S7/M7-300/400 or C7-300 CPU, if it is in the RUN, HALT
operating mode or in a startup.
SFB 21 RESUME Trigger resume operation of an S7-400-CPU if it is in STOP mode.
SFBs for Querying the Operating Status
With SFBs for querying the operating status, you can obtain information about the
operating status of a remote device.
With SFB "STATUS," data exchange is unilateral while with SFB "USTATUS," it is
bilateral.
Block S7-400 Brief Description
SFB 22 STATUS Supplies the operating state of a communication partner (S7-400-CPU,
M7-300/400) on user request.
SFB 23 USTATUS Receives the operating state of an S7-400-CPU when it changes its
operate state, if the corresponding connection attribute (send operating
state messages) has been set.
SFC/FCs for Querying Connections
Block S7-400 Block S7-300 Brief Description
SFC 62 CONTROL Querying the state of a connection which belongs to an
instance of an SFB/FB.
FC 62 C CNTRL Querying a connection state through the connection ID
Tip:
You can also use SFC 87 C_DIAG to perform a diagnosis of the actual connection
state (only for S7-400).
Sample Program
A sample program for S7-400 which shows the use of the SFBs for the S7
communication is supplied with STEP 7. This sample program is called
step7\examples\com_sfb. It is included under the sample programs in the path
folder "..\STEP7\Examples\ZDT01_10".