97BPLC concepts
4.1 Execution of the user program
S7-1200 Programmable controller
System Manual, 11/2011, A5E02486680-05
63
You can specify whether digital and analog I/O points are to be automatically updated and
stored in the process image. If you insert a module in the device view, its data is located in
the process image of the CPU (default). The CPU handles the data exchange between the
module and the process image area automatically during the update of the process image.
To remove digital or analog points from the process-image automatic update, select the
appropriate device in Device configuration, view the Properties tab, expand if necessary to
locate the desired I/O points, and then select "IO addresses/HW identifier". Then change the
entry for "Process image:" from "Cyclic PI" to "---". To add the points back to the process-
image automatic update, change this selection back to "Cyclic PI".
You can immediately read physical input values and immediately write physical output
values when an instruction executes. An immediate read accesses the current state of the
physical input and does not update the process image input area, regardless of whether the
point is configured to be stored in the process image. An immediate write to the physical
output updates both the process image output area (if the point is configured to be stored in
the process image) and the physical output point. Append the suffix ":P" to the I/O address if
you want the program to immediately access I/O data directly from the physical point instead
of using the process image.
The CPU supports distributed I/O for both PROFINET and PROFIBUS networks (Page 393).
4.1.1
Operating modes of the CPU
The CPU has three modes of operation: STOP mode, STARTUP mode, and RUN mode.
Status LEDs on the front of the CPU indicate the current mode of operation.
●
In STOP mode, the CPU is not executing the program. You can download a project.
●
In STARTUP mode, the startup OBs (if present) are executed once. Interrupt events are
not processed during the startup mode.
●
In RUN mode, the program cycle OBs are executed repeatedly. Interrupt events can
occur and be processed at any point within the RUN mode. Some parts of a project can
be downloaded in RUN mode (Page 650).
The CPU supports a warm restart for entering the RUN mode. Warm restart does not include
a memory reset. All non-retentive system and user data are initialized at warm restart.
Retentive user data is retained.
