Quick review
1.1 Basic information about how the CPU works
Getting started with S7-1200
Getting Started, 11/2009, A5E02486791-01
9
1.1.2 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
not processed during the startup mode.
● In RUN mode, the scan cycle is executed repeatedly. Interrupt events can occur and be
processed at any point within the program cycle phase.
Note
You cannot download a project while the CPU is in RUN mode. You can download your
project only when the CPU is in STOP mode.
The CPU does not have a physical switch for changing the operating modes (STOP or
RUN). When you configure the CPU in the device configuration, you configure the start-up
behavior in the properties of the CPU. The STEP 7 Basic provides an operator panel for
changing the operating mode of the onli
ne CPU (Page 56).
Use the button on the operator panel to change the operating
mode (STOP or RUN). The operator panel also provides an
MRES button for resetting the memory.
The color of the RUN/STOP indicator shows the current
operating mode of the CPU:
Yellow indicates STOP mode.
Green indicates RUN mode.
Flashing indicates STARTUP mode.
To Next Page
Loading...
