Siemens SIMATIC S7-300 Series Reference Manual page 155

Tips and Tricks
Tip on the Parameter "Monitoring time for ..." in STEP 7
Configure the parameters for "Monitoring time
S for parameter download to module"
S ready message by module"
the highest values if you are not certain of the times required on the S7-300.
CPU 31x-2DP is DP Master
You can also set power-up time monitoring
for the DP slaves with the "Transfer of
parameters to modules" parameter.
This means that the DP slaves must be powered up and configured by the CPU (as DP
master) in the set time.
FM in a Distributed Configuration in an ET 200M (CPU 31x-2 is DP Master)
If you operate an FM 353/354/355 in an ET 200M with IM 153-2 and remove and
reinsert the FM in ET 200M, you must perform a cold restart (power off/on) in the
ET 200M.
Reason: The CPU does not rewrite the parameters to the FM unless the ET200M
is initialized with "POWER ON".
The Retentive Feature of Data Blocks
You must note the following for the retentivity of data areas in data blocks:
PLC S7-300, CPU Specifications CPU 312 IFM to CPU 318-2 DP
A5E00111190-01
CPU 318-2 is DP Master
You can set power-up time monitoring for
the DP slaves with both of the above
parameters.
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