Siemens OP7 Equipment Manual page 124

Before
Before commissioning the OP, take note of the following:
commissioning
Caution
!
15-2
With the SIMATIC S5, compression of the internal program memory of
the PLC (PU "Compress" function, integrated COMPR FB) is not al-
lowed when an OP is connected. Compression modifies the absolute ad-
dresses of the blocks in the program memory. As the OP reads the ad-
dress list only during start-up, it does not detect any address modifica-
tions and accesses the wrong memory areas.
If compression is inevitable during routine operation, turn off the OP
prior to compression.
Do not disconnect while circuit is live unless location is known to be
nonhazardous.
Equipment Manual OP7, OP17
Release 04/99