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Functions of the IM 151-7 CPU

8-22

ET 200S IM 151-7 CPU Interface Module

A5E00058783-04

Local data

The following are stored as local data:

 The temporary variables of code blocks

 The start information of the organization blocks

 Transfer parameters

 Intermediate results

Temporary variables

When creating blocks, you can declare temporary variables (TEMP) which are only

available while the block is being processed and are then overwritten again. This

local data has a fixed length for each OB. The local data must be initialized before

the first read access operation. Furthermore, each organization block requires 20

bytes for its start information. Local data is accessed faster than data in the DBs.

The IM 151-7 CPU has memory for the temporary variables (local data) of blocks

that have just been processed. This memory is divided equally between the priority

classes. Each priority class has its own local data area.

Caution

All temporary variables (TEMP) of an OB and its subordinate blocks are stored in

the local data. The local data area could overflow if you use a large number of

nesting levels for block processing.

The IM 151-7 CPU changes to the STOP mode if you exceed the permitted

quantity of local data in a priority class.

Take into consideration the amount of local data required by the synchronous fault

OBs. In each case, the local data requirement is assigned to the responsible

priority class.

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Siemens ET 7Y Series Especificaciones Pagina 134