Siemens SIMATIC ET 200SP System Manual page 142

UPDAT_PI: updates the process image partition of the inputs
With this instruction you read the signal states from the input modules into the process
image partition of the inputs (PIPI).
UPDAT_PO: updates the process image partition of the outputs
With this instruction you transfer the process image partition of the outputs to the output
modules.
Synchronous cycle interrupt OB
In the synchronous cycle interrupt OBs, you use the "SYNC_PI" and "SYNC_PO" operations
to update the process image partitions of the operations. For additional information on the
synchronous cycle interrupt OBs, refer to the STEP 7 Online Help.
Direct I/O access to the inputs and outputs of the module
As an alternative to access via the process image, you can directly access the I/O (write and
read access) if this is necessary for program-related reasons. Direct (write) access to I/O
also writes to the process image. This prevents a subsequent output of the process image
from again overwriting the value written by direct access.
Reference
Additional information on process image partitions is available in the function manual, Cycle
and response times (http://support.automation.siemens.com/WW/view/en/59193558).
Distributed I/O system
System Manual, 09/2019, A5E03576849-AJ
Configuring
7.2 Configuring the CPU
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