Technical data

Appendix
27.1 Operating Modes
Programming with STEP 7
558 Manual, 05/2010, A5E02789666-01
Other Operating Modes
If the CPU is not ready for operation, it is in one of the following modes:
• Off, in other words, the power supply is turned off.
• Defective, in other words, a fault has occurred.
To check whether the CPU is really defective, switch the CPU to STOP and turn the power
switch off and then on again. If the CPU starts up, display the diagnostic buffer to analyze the
problem. If the CPU does not start up it must be replaced.
Operating Mode Transitions
The following figure shows the operating modes and mode transitions for S7-300 and S7-400
CPUs:
The table shows the conditions under which the operating modes can change.
Transition Description
1. After you turn on the power supply, the CPU is in STOP mode.
2. The CPU changes to STARTUP mode:
• After the CPU is changed to RUN or RUN-P using the key switch or by the programming
device.
• After a startup triggered automatically by turning on the power.
• If the RESUME or START communication function is executed.
In both cases the key switch must be set to RUN or RUN-P.
3. The CPU changes back to STOP mode when:
• An error is detected during the startup.
• The CPU is changed to STOP by the key switch or on the programming device.
• A stop command is executed in the startup OB.
• The STOP communication function is executed.
4. The CPU changes to HOLD mode when a breakpoint is reached in the startup program.
5. The CPU changes to STARTUP mode when the breakpoint in a startup program was set and
the "EXIT HOLD" command was executed (test functions).
6. The CPU changes back to STOP mode when:
• The CPU is changed to STOP with the key switch or by the programming device.
• The STOP communication command is executed.
7. If the startup is successful, the CPU changes to RUN.