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6.2.3
Process images and process image partitions
6.2.3.1
Process image - overview
Process image of the inputs and outputs
The process image is a memory area of the CPU and includes an image of the signal states
of the input/output modules. At the start of the cyclic program, the CPU transfers the signal
states of the input modules to the process image of the inputs. At the end of the cyclic
program, the CPU transfers the process image of the outputs as a signal state to the output
modules. You access this process image memory area in the user program by addressing
the operand areas inputs (I) and outputs (O).
Advantages of the process image
A process image offers the advantage that you can access a consistent image of the
process signals during cyclic program execution. If a signal state at an input module changes
during program processing, the signal state is retained in the process image. The process
image is not updated until the next cycle.
You can only assign the addresses of a module to a single process image partition.
32 process image partitions
The overall process image is subdivided into up to 32 process image partitions (PIP).
The user program updates the PIP 0 in each program cycle (automatic update). The PIP 0 is
assigned to OB 1.
You can assign the process image partitions PIP 1 to PIP 31 to the other OBs during
configuration of the input/output modules in STEP 7.
Distributed I/O system
System Manual, 12/2016, A5E03576849-AG
Configuring
6.2 Configuring the CPU
147
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