Technical data

Structure and Use of the CPU Memory

Function Manual, 01/2013, A5E03461664-01

Glossary

Bit memory

Bit memory is a memory area of the CPU, which can be addressed from any code block (FC,

FB, OB). You have read/write access to this memory area. The bit memory area can be used

to store temporary results, for example.

Counters

In STEP 7, counting tasks are performed using counters. You can modify the contents of the

"counter cells" using STEP 7 instructions (for example, count up/down).

Data block

Data blocks store information for the program. They can be defined in two ways: either that

all code blocks can access them (global data block), or that they are assigned to a specific

FB or SFB (instance data block).

Data log

Data logs are csv files for the storage of tag values. The data logs are saved on the

SIMATIC memory card in the "\datalogs" directory. Data records of tag values are written to

a data log by means of instructions in the user program

Global data block (DB)

Every function block, every function, and every organization block can read the data from a

global data block, or write its own data to a global data block. This data is retained in the

data block, even when the data block is exited.

Instance data block (IDB)

A data block is assigned to each call of a function block in the STEP 7 user program. The

instance data block stores the values of input, output and in/out parameters, as well as local

block data.

Local data

This memory area accepts the temporary local data of a block for the duration of processing.

Memory reset

During memory reset the CPU is shifted into the configured initial state.