Update Process Image Partitions In The User Program - Siemens SIMATIC S7-1500 System Manual

Configuring
6.1 Configuring the CPU
6.1.3.3

Update process image partitions in the user program

Requirements
As an alternative to the automatic updating and to updating by assignment to an OB, you
can use the instruction "UPDAT_PI" or the instruction "UPDAT_PO" at the start or the at the
end of the respectively assigned OB to update the process image. In STEP 7, these
instructions are available on the "Instructions" Task Card under "Extended instructions" and
may be called from any point in the program.
Requirements for updating process image partitions with the "UPDAT_PI" and "UPDAT_PO"
instructions:
● The process image partitions cannot be assigned to any OB, i.e. they cannot be
automatically updated.
● PIP 0 (automatic update) can likewise not be updated with the "UPDAT_PI" and
"UPDAT_PO" instructions.
UPDAT_PI: Update 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: Update process image partition of the outputs
With this instruction you transmit the process image partition of the outputs to the output
modules.
Is ochronous mode interrupt OBs
In the isochronous mode interrupt OBs you use the instructions "SYNC_PI" and "SYNC_PO"
to update the process image partitions. Additional information on isochronous mode interrupt
OBs is available in the STEP 7 online help.
Direct I/O access to the inputs and outputs of the module
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. A direct (write)
I/O access also writes the process image. This prevents the situation where a subsequent
output of the process image overwrites the value written via direct access again.
Reference
Additional information on process image partitions is available found in the function manual,
Cycle and response times (http://support.automation.siemens.com/WW/view/en/59193558).
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Automation system
System Manual, 09/2016, A5E03461182-AD