Siemens SIMATIC S5 Manual page 262

Application of the Function Block
Special features of the commands KS, PA and AE
KS: the command KS (cold restart) must only be used in one of the start-up OBs
(OB 20, OB 21 or OB 22).
The command KS must be used to assign parameters:
– when the module is first put into operation
– if you are not sure that the memory of the IP 244 has been backed up
continuously.
PA/AE: the commands PA (assign parameters) and AE (change parameters) require at
least two clock cycles before they are processed. This means that FB 162 must
be called several times until parameter ANST is reset (with direct parameter
assignment) or until the command in data word DW 1 of data block DB-A is cleared
(with indirect parameter assignment).
The command PA must only be used when:
– the module has already been put into operation,
– you are sure that the data in the memory of the module was backed up while
the power supply was off (i.e. the CC or EU must be equipped with a
back-up battery and the IP 244 must be inserted in a battery backed slot),
– the module has not been removed from the rack since its previous
operation.
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IP244
C79000–B8576–C861–02