Information For The Changeover To The Technology Cpu; Changed Behavior Of Certain Sfcs - Siemens SIMATIC S7-300 Manual

Information for the Changeover to the Technology CPU

9.2 Changed behavior of certain SFCs

... then please read the following information regarding migration to the Technology CPU
9.2 Changed behavior of certain SFCs
9.2
SFC 13, SFC 56 and SFC 57 which work asynchronously...
Some of the SFCs that work asynchronously, when used on CPUs 312 IFM to 318-2 DP,
were always, or under certain conditions, processed after the first call ("quasi-synchronous").
On the Technology CPU, these SFCs actually run asynchronously. Asynchronous
processing may cover multiple OB1 cycles. As a result, a wait loop may turn into an endless
loop within an OB.
The following are affected:
• SFC 13 "DPNRM_DG"
Note
In the user program, the job should merely be started in OB 82. The data should be
evaluated in the cyclical program, taking account of the BUSY bits and the value returned in
RET_VAL.
Tip
If you are using a Technology CPU, we recommend that you use SFB 54, rather than SFC
13 "DPNRM_DG".
• SFC 56 "WR_DPARM"; SFC 57 "PARM_MOD"
Note
If you are using SFC 56 "WR_DPARM" or SFC 57 "PARM_MOD", you should always
evaluate the SFCs' BUSY bit.
9-2
On CPUs 312 IFM to 318-2 DP, this SFC always works "quasi synchronously" when it is
called in OB 82. On the Technology CPU, it generally works asynchronously.
On CPUs 312 IFM to 318-2 DP, these SFCs always work "quasi-synchronously" during
communication with centralized I/O modules and always work synchronously during
communication with distributed I/O modules.
S7-300 CPU Data: CPU 315T-2 DP
Manual, 12/2005, A5E00427933-02