Technical data

Appendix
27.1 Operating Modes
Programming with STEP 7
Manual, 05/2010, A5E02789666-01 565
Startup Activities
The following table shows which activities are performed by the CPU during startup:
Activities in Order of Execution In Warm Restart In Cold Restart In Hot Restart
Clear I stack/B stack X X 0
Clear volatile memory bits, timers, counters X 0 0
Clear all memory bits, timers, counters 0 X 0
Clear process-image output table X X selectable
Reset outputs of digital signal modules X X selectable
Discard hardware interrupts X X 0
Discard time-delay interrupts x x 0
Discard diagnostic interrupts X X X
Update the system status list (SZL) X X X
Evaluate module parameters and transfer to
modules or transfer default values
X X X
Execution of the relevant startup OB X X X
Execute remaining cycle (part of the user
program not executed due to the power down)
0 0 X
Update the process-image input table X X X
Enable digital outputs (cancel OD signal) after
transition to RUN
X X X
X means is performed
0 means is not performed
Aborting a Startup
If an error occurs during startup, the startup is aborted and the CPU changes to or remains in
STOP mode.
An aborted warm restart must be repeated. After an aborted restart, both a warm restart and a hot
restart are possible.
A startup (restart (warm restart) or hot restart) is not executed or it is aborted in the following
situations:
• The operating mode switch of the CPU is set to STOP.
• A memory reset is requested.
• A memory card with an application code that is not permitted for STEP 7 is plugged in (for
example, STEP 5).
• More than one CPU is inserted in the single processor mode.
• If the user program contains an OB that the CPU does not recognize or that has been disabled.
• If, after power on, the CPU recognizes that not all the modules listed in the configuration table
created with STEP 7 are actually inserted (difference between preset and actual parameter
assignment not permitted).