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Introduction to STEP 5
7.5
Processing Blocks
Earlier sections in this chapter described how to use blocks. Chapter 8 introduces all of the
operations required to work with blocks. Blocks that you have already programmed can only be
changed in the test mode. The individual ways to change blocks are only briefly described. The
operating instructions of the programmers used explain the necessary steps in detail.
7.5.1
Changing Programs
Program changes are not possible in the safety mode.
In the test mode, program changes can be executed with the following programmer functions
independent of the type of block.
•
INPUT
•
OUTPUT
•
STATUS
These three programmer functions make it possible for you to make the following types of changes:
•
Delete, insert, or overwrite statements.
•
Insert or delete segments.
7.5.2
Changing Blocks
Program changes refer to changing the contents of a block. You can also delete or overwrite a
complete block. When you delete a block, it is not deleted from the program memory but simply
becomes invalid. You cannot enter new information in the memory location of an invalid block. This
may cause a new block not to be accepted. If a new block is not accepted, then the PG transmits
the "no space available" error message. You can delete this message by compressing the
programmable controller memory. Compressing is not possible in the RUN mode of safety operation.
7.5.3
Compressing the Program Memory
Figure 7-15 illustrates what takes place in the program memory during a COMPRESS operation.
Internally, one block is shifted per cycle.
Program memory
Valid
blocks
Invalid
blocks
Input not
possible
PB
7-30
RAM
Compress
Available
memory space
Figure 7-15. Compressing the Program Memory
Program memory
RAM
EWA 4NEB 812 6210-02
S5-95F
Input
possible
PB
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