Technical data

Table Of Contents
SFCs for Diagnostics
System Software for S7-300/400 System and Standard Functions - Volume 1/2
A5E00709327-01
13-23
13.7 Identifying the Bus Topology of a DP Master System
with SFC 103 "DP_TOPOL"
Description
Call SFC 103 "DP_TOPOL" with its diagnostics repeaters to initiate the
identification of the bus topology of a selected a DP master system. All diagnostics
repeaters connected to a DP master system are addressed when SFC 103 is
called.
Note
The topology of only one DP master system can be identified at a given time.
The identification of the topology is a prerequisite for a detailed display of the error
location in the event of a line error. After the installation or any changes to the
physical structure of a DP master system, once again identify the topology with
SFC 103.
Changes to the physical structure includes:
Change in cable lengths
Addition or removal of nodes or of components with repeater function
Change in node addresses
Each diagnostic repeater enters the result (PROFIBUS address of all nodes and
their absolute distance to the diagnostic repeater) in a topology table. You can read
these values under STEP 7.
We recommend to call SFC 103 in OB1 or in a watchdog interrupt OB. An S7-300
does not allow this call in one of the startup OBs.
The SFC writes error messages returned by the diagnostic repeater to the outputs
DPR and DPRI for as long as the SFC is being executed. If more than one
diagnostic repeater in the selected DP master system reports an error, the SFC
enters in DPR and DPRI only information relevant to the diagnostic repeater that
has first generated an error message. Call SFC 13 "DPNRM_DG" or STEP 7 to
read the complete diagnostic information. The value of outputs DPR and DPRI is
NULL if no error is reported by a diagnostic repeater.
If you want to trigger another topology determination after an error has occurred,
you must first reset SFC103. To do this, call the SFC with REQ=0 and R=1.