Memory Areas, Addressing And Data Types - Siemens SIMATIC S7-1200 Manual

4.3

Memory areas, addressing and data types

The CPU provides the following memory areas to store the user program, data, and
configuration:
● Load memory is non-volatile storage for the user program, data and configuration. When
● Work memory is volatile storage for some elements of the user project while executing
● Retentive memory is non-volatile storage for a limited quantity of work memory values.
An optional SIMATIC memory card provides an alternative memory for storing your user
program or a means for transferring your program. If you use the memory card, the CPU
runs the program from the memory card and not from the memory in the CPU.
Use the optional SIMATIC memory card either as a program card or as a transfer card:
● Use the transfer card to copy your project to multiple CPUs without using STEP 7 Basic.
● The program card takes the place of CPU memory; all of your CPU functions are
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a project is downloaded to the CPU, it is first stored in the Load memory area. This area
is located either in a memory card (if present) or in the CPU. This non-volatile memory
area is maintained through a power loss. The memory card supports a larger storage
space than that built-in to the CPU.
the user program. The CPU copies some elements of the project from load memory into
work memory. This volatile area is lost when power is removed, and is restored by the
CPU when power is restored.
The retentive memory area is used to store the values of selected user memory locations
during power loss. When a power down occurs, the CPU has enough hold-up time to
retain the values of a limited number of specified locations. These retentive values are
then restored upon power up.
The transfer card copies a stored project from the card to the memory of the CPU. You
must remove the transfer card after copying the program to the CPU.
controlled by the program card. Inserting the program card erases all of the internal load
memory of the CPU (including the user program and any forced I/O). The CPU then
executes the user program from the program card.
The program card must remain in the CPU. If you remove the program card, the CPU
goes to STOP mode.
4.3 Memory areas, addressing and data types
The CPU supports only a preformatted
SIMATIC memory card.
To insert a memory card, open the top
CPU door and insert the memory card in
the slot. A push-push type connector
allows for easy insertion and removal. The
memory card is keyed for proper
installation.
Check that the memory card is not write-protected. Slide the
protection switch away from the "Lock" position.
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