Technical data

Appendix

27.1 Operating Modes

Programming with STEP 7

Manual, 05/2010, A5E02789666-01 561

27.1.3 STARTUP Mode

Before the CPU can start processing the user program, a startup program must first be executed.

By programming startup OBs in your startup program, you can specify certain settings for your

cyclic program.

There are three types of startup: warm restart, cold restart, and hot restart. A hot restart is only

possible on S7-400 CPUs. This must be set explicitly in the parameter set for the CPU using STEP

The features of the STARTUP mode are as follows:

• The program in the startup OB is processed (OB100 for warm restart, OB101 for hot restart,

OB102 for cold restart).

• No time-driven or interrupt driven program execution is possible.

• Timers are updated.

• Runtime meters start running.

• Disabled digital outputs on signal modules (can be set by direct access).

Warm Restart

A warm restart is always permitted unless the system has requested a memory reset. A warm

restart is the only possible option after:

• Memory reset

• Downloading the user program with the CPU in STOP mode

• I stack/B stack overflow

• Warm restart aborted (due to a power outage or changing the mode selector setting)

• When the interruption before a hot restart exceeds the selected time limit.

Manual Warm Restart

A manual warm restart can be triggered by the following:

• The mode selector

(the CRST/WRST switch - if available - must be set to CRST)

• The corresponding command on the programming device or by communication functions

(if the mode selector is set to RUN or RUN-P)