97BPLC concepts
4.1 Execution of the user program
S7-1200 Programmable controller
System Manual, 11/2011, A5E02486680-05
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4.1.6
CPU memory
Memory management
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
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.
●
Work memory is volatile storage for some elements of the user project while executing
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.
●
Retentive memory is non-volatile storage for a limited quantity of work memory values.
The retentive memory area is used to store the values of selected user memory locations
during power loss. When a power down or power loss occurs, the CPU restores these
retentive values upon power up.
To display the memory usage for the current project, right-click the CPU (or one of its blocks)
and select "Resources" from the context. To display the memory usage for the current CPU,
double-click "Online and diagnostics", expand "Diagnostics", and select "Memory".