Processing Blocks; Changing Programs; Changing Blocks; Compressing The Program Memory - Siemens SIMATIC S5-90U System Manual

S5-90U/S5-95U
7.4

Processing Blocks

Earlier sections in this chapter described how to use blocks. Chapter 8 introduces all of the
operations required to work with blocks.
You can change any blocks that have already been programmed. The following sections will deal
only briefly with the different ways you can change blocks. Refer to your STEP 5 manual for more
detailed information on changing blocks.
7.4.1

Changing Programs

You can use the following programmer functions to make program changes with any block type.
• 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.
7.4.2

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.
7.4.3

Compressing the Program Memory

Figure 7-8 illustrates what takes place in the program memory during a COMPRESS operation.
Internally, one block is shifted per cycle.
Program memory
Valid
blocks
Invalid
Input not
possible
PB
EWA 4NEB 812 6115-02b
RAM
Compress
Available
memory space
Figure 7-8. Compressing the Program Memory
Introduction to STEP 5
Program memory
RAM
Input
possible
PB
7-17