Cold Start / Warm Restart / Hot Restart - Siemens SIMATIC S7-400 Manual

2.6

Cold start / Warm restart / Hot restart

Cold start
● During a cold restart, all data (process image, bit memory, timers, counters and data
● 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
● 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
Hot Restart
● When a hot restart is performed, all data and the process image retain their last valid
● 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
Operating Sequence at Restart (Warm Restart)
1. Set the mode selector to STOP.
2. Set the switch to RUN.
Whether the CPU executes a warm restart or hot restart depends on the CPU parameter
settings.
S7-400 Automation System, CPU Specifications
Manual, 10/2006, 6ES7498-8AA04-8BA0
blocks) are reset to the start values stored in the program (load memory), irrespective of
whether they were configured as retentive or non-retentive.
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.
mode.
value.
mode.
Result: The STOP LED is lit.
Structure of a CPU 41x
2.6 Cold start / Warm restart / Hot restart
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