Configuring
7.2 Configuring the CPU
Distributed I/O system
System Manual, 09/2019, A5E03576849-AJ
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7.2.3 Process images and process image partitions
7.2.3.1 Process image - overview
Process image of the inputs and outputs
The process image input and output is an image of the signal states. The CPU transfers the
values from the input and output modules to the process image input and output. At the start
of the cyclic program, the CPU transfers the process image output as a signal state to the
output modules. Afterwards the CPU transfers the signal states of the input modules to the
process image input.
Advantages of the process image
The process image accesses 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 CPU does not update the process
image until the next cycle.
You can only assign the addresses of a module to a single process image partition.
32 process image partitions
By means of process image partitions, the CPU synchronizes the updated inputs/outputs of
particular modules with defined user program sections.
The overall process image is subdivided into up to 32 process image partitions (PIP).
The CPU updates PIP 0 in each program cycle (automatic update) and assigns it 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.
After the OB has been started, the CPU updates the assigned process image partition for
inputs and reads in the process signals. At the end of the OB the CPU writes the outputs of
the assigned process image partition directly to the peripheral outputs without having to wait
for the completion of the cyclic program processing.
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