Technical data

Appendix
27.8 Setting the Operating Behavior
Programming with STEP 7
678 Manual, 05/2010, A5E02789666-01
27.8 Setting the Operating Behavior
This chapter explains how you can modify certain properties of S7-300 and S7-400 programmable
controllers by setting system parameters or using system functions (SFCs).
You will find detailed information on the module parameters in the STEP 7 online help and in the
following manuals:
• "S7-300 Programmable Controller, Hardware and Installation" Manual
• "S7-300, M7-300 Programmable Controllers, Module Specifications" Reference Manual
• "S7-400, M7-400 Programmable Controllers, Module Specifications" Reference Manual
You will find all you need to know about SFCs in the "System Software for S7-300 and S7-400,
System and Standard Functions" Reference Manual.
Addressing DP Standard Slaves
If you want to exchange data longer than 4 bytes with DP standard slaves, you must use special
SFCs for this data exchange.
CPUs that support the exchange of consistent data (> 4 bytes) by means of the I/O area do not
need SFCs 14/15 (see Distributed Reading and Writing of Consistent Data).
SFC Purpose
Assigning parameters to modules
SFC15 DPWR_DAT Transfers any data to the addressed signal module
Reading out diagnostic information
SFC13 DPNRM_DG Reads the diagnostic information (asynchronous read access)
SFC14 DPRD_DAT Reads consistent data (length 3 or greater than 4 bytes)
When a DP diagnostic frame arrives, a diagnostic interrupt with 4 bytes of diagnostic data is
signaled to the CPU. You can read out these 4 bytes using SFC13 DPNRM_DG.