Siemens SIMATIC PCS 7 Configuration Manual page 187

What situations will prevent online downloads of changes?
It is no longer possible to download changes if the following conditions are present:
● A used block type has been replaced by a new version that contains structural changes,
for example, due to the addition of I/Os and/or messages. An exception to this is the CPU
410-5H process automation with a firmware version from V8.1 which supports the function
"Type Change in Run" (TCiR). For more information, refer to the section "Updating block
types (Page 159)").
● DB and FC number areas have been compressed during compilation using the menu
command Options > Settings > Compile/Download... > Option: "Compress". DBs and FCs
will be assigned a new numbering sequence in this case.
● When a modified program was downloaded to a different CPU prior to the download of
changes, for example, for debugging purposes. In this case, the time stamp no longer
matches the time stamp of the original CPU. An exception to this is provided where the
"Download to Test CPU" option is used in the "Download S7" dialog box. In this case the
download ID and the comparison time stamp are retained. You can still therefore transfer
the program to the original CPU by downloading changes.
● If you resort to an archived program that is not the original from the most recent download
(time stamp comparison).
Note
Refer to the online help for the CFC Editor and to the "Downloading changes online
(Page 287)" section for additional information.
Compendium Part A - Configuration Guidelines (V8.2)
Configuration Manual, 08/2016, A5E38166869-AA
Compiling and downloading
9.2 Downloading the user program
187