Operating Modes Of The Cpu - Siemens SIMATIC S7-1200 Manual

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4.2 Operating modes of the CPU

STARTUP
A
B
C Executes the startup OBs
D Copies the state of the physical inputs to I
E
F
You can change the default behavior for a module by removing it from this automatic update
of I/O. You can also immediately read and write digital and analog I/O values to the modules
when an instruction executes. Immediate reads of physical inputs do not update the process
image input area. Immediate writes to physical outputs update both the process image
output area and the physical output point.
4.2 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, and you can download a project.
● In STARTUP mode, the CPU executes any startup logic (if present). Interrupt events are
● In RUN mode, the scan cycle is executed repeatedly. Interrupt events can occur and be
The CPU supports the warm restart method for entering the RUN mode. Warm restart does
not include a memory reset, but a memory reset can be commanded from the programming
software. A memory reset clears all work memory, clears retentive and non-retentive
memory areas, and copies load memory to work memory. A memory reset does not clear the
diagnostics buffer or the permanently saved IP address. All non-retentive system and user
data are initialized at warm restart.
50
Clears the input (or "I") memory
Initializes the outputs with either the last
value or the substitute value
memory
Stores any interrupt events into the queue to
be processed in RUN mode
Enables the writing of the output (or "Q")
memory to the physical outputs
not processed during the startup mode.
processed at any point within the program cycle phase. Some parts of a project can be
downloaded in RUN mode.
RUN
①
Writes Q memory to the physical outputs
②
Copies the state of the physical inputs to I
memory
③
Executes the program cycle OBs
④
Performs self-test diagnostics
⑤
Processes interrupts and communications
during any part of the scan cycle
Manual, 11/2011, A5E02486774-04
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