Siemens S7-1200 System Manual page 810

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14.12 Downloading in RUN mode

Configuring amount of reserved memory for new blocks

The default memory reserve size for new data blocks is 100 bytes. When you create a new

block, it has 100 bytes available in reserve. If you want the memory reserve size to be

different for new blocks, you can change the setting in the PLC programming settings:

1. From STEP 7, select the Options > Settings menu command.

2. From the Settings dialog, expand "PLC programming" and select "General".

3. In the "Download without reinitialization" section, enter the number of bytes for the

memory reserve.

When you create new blocks, STEP 7 uses the memory reserve configuration that you

entered for the new blocks.

Restrictions

The following restrictions apply to editing and downloading blocks in RUN mode:

● Extending the block interface by adding new tags and downloading in RUN mode is only

available for optimized blocks (Page 176).

● You cannot change the structure of a block and download the changed block in RUN

mode without reinitializing. Adding new members to a Struct (Page 117) tag, changing

tag names, array sizes, data types, or retentive status all require that you reinitialize the

block if you download it in RUN mode. The only modifications to existing block tags that

you can perform and still download the block in RUN mode without reinitialization are

changes to start values (data blocks), default values (function blocks) or comments.

The ability to modify blocks and download them in RUN mode is new with V4.0 of the

S7-1200 CPU. Prior to V4.0, you could only download modified blocks in STOP mode.

● You cannot download more new block tags in RUN mode than the memory reserve can

accommodate.

● You cannot download more new retentive block tags in RUN mode than the retentive

memory reserve can accommodate.