Process Images And Process Image Partitions; Process Image - Overview - Siemens Simatic ET200pro Operating Instruction

4.2.3

Process images and process image partitions

4.2.3.1

Process image - overview

Process image of the inputs and outputs
When the user program addresses the input (I) and output (O) operand areas, it does not
query the signal states directly from the I/O modules. Instead, it accesses a memory area of
the CPU. This memory area contains an image of the signal states and is called the process
image.
Advantages of the process image
A process image allows you to access a consistent image of 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.
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.
For the CPU 1516pro-2 PN, the overall process image is subdivided into up to 32 process
image partitions (PIP).
PIP 0 (automatic update) is automatically updated in each program cycle and is assigned to
OB 1.
Process image partitions PIP 1 through PIP 31 can be assigned to the other OBs. In STEP
7, this assignment occurs during configuration of the input/output modules.
After the OB has been started, the assigned process image partition for inputs is updated by
the system and the process signals are read in. At the end of the OB, the outputs of the
assigned process image partition are written directly to the peripheral outputs by the system
without having to wait for the completion of the cyclic program processing.
CPU 1516pro-2 PN (6ES7516-2PN00-0AB0)
Operating Instructions, 09/2016, A5E35873416-AA
Configuring
4.2 Configuring the CPU
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