Structure of a CPU 41x
2.6 Cold start / Warm restart / Hot restart
S7-400 Automation System, CPU Specifications
Manual, 10/2006, 6ES7498-8AA04-8BA0
2-15
2.6 Cold start / Warm restart / Hot restart
Cold start
● During a cold restart, all data (process image, bit memory, timers, counters and data
blocks) are reset to the start values stored in the program (load memory), irrespective of
whether they were configured as retentive or non-retentive.
● Corresponding startup OB is OB 102
● Program execution is restarted at the beginning (OB 102 or OB 1).
Restart (Warm Restart)
● A warm restart resets the process image and the non-retentive flags, timers, times and
counters.
Retentive flags, times and counters retain their last valid value.
All data blocks assigned the "Non Retain" attribute are reset to the load values. The
remaining data blocks retain their last valid value.
● Corresponding startup OB is OB 100
● Program execution is restarted at the beginning (OB 100 or OB 1).
● After a power supply interruption, the warm restart function is only available in backup
mode.
Hot Restart
● When a hot restart is performed, all data and the process image retain their last valid
value.
● Program execution is resumed at the breakpoint.
● The outputs do not change their status until the current cycle is completed.
● Corresponding startup OB is OB 101
● After a power supply interruption, the hot restart function is only available in backup
mode.
Operating Sequence at Restart (Warm Restart)
1. Set the mode selector to STOP.
Result: The STOP LED is lit.
2. Set the switch to RUN.
Whether the CPU executes a warm restart or hot restart depends on the CPU parameter
settings.
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