Siemens SIMATIC S7-1500 System Manual page 109

Configuring
7.8 Process images and process image partitions
Direct I/O access to the inputs and outputs of the IO devices
You also have direct read and write access to the I/O as an alternative to access via the
process image, should direct access be required for programming reasons. Direct (write) I/O
access also writes to the process image. This prevents a subsequent output of the process
image from again overwriting the value written by direct access.
Additional information
You can find more information on process image partitions in the Cycle and response times
(https://support.industry.siemens.com/cs/ww/en/view/59193558) function manual.
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SIMATIC Drive Controller
System Manual, 11/2019, A5E46600094-AA