What is the difference between a restart (warm restart), cold restart and hot restart of a S7-400 CPU?
In the startup program, you can define specific presettings for your cyclic program by programming startup OBs accordingly.
There are three types of startup:
|Startup mode||Brief description|
|Restart (warm restart)||Program processing starts anew. Retentive data is retained.|
|Cold restart||Current data is discarded and program processing begins again with the start values.|
|Hot restart||Once power is resumed, the program continues at the point at which it was interrupted.|
In operating mode "STARTUP":
- The program is processed in the startup OB (OB 100 for restart (warm restart), OB 101 for hot restart and OB 102 for cold restart).
- Time- and alarm-controlled program processing is not possible.
- Times are updated.
- The runtime meter runs.
- The digital outputs on signal modules are blocked, but can be set via direct access.
In a restart (warm restart), program processing restarts at the beginning of the program with a "basic setting" of the system data and user address areas.
- The process image and the non-retentive markers, timers and counters are reset. Retentive markers, timers and counters each retain their last valid value. All data blocks parameterized with the property "Non Retain" are reset to the loaded values. The other data blocks each retain their last valid value.
- Program processing starts again at the beginning (startup OB or OB 1).
- If the power supply is interrupted, a warm restart is only possible in buffered mode. If you are operating your CPU without backup battery, the CPU is automatically reset completely and then restarted (warm restart) when you switch on or power returns after a POWER OFF.
A restart (warm restart) is always permissible unless the system demands an overall reset. In the following cases only a restart (warm restart) is possible after:
- Overall reset.
- Loading of the user program in the STOP mode of the CPU.
- USTACK/BSTACK overflow.
- Interruption of the restart (warm restart) through POWER OFF or via mode switch.
- Exceeding of parameterized interruption time limit for restart.
Order of operations for restart (warm restart):
You can trigger a manual restart (warm restart):
- Via the mode selector switch
(if available, the CRST/WRST switch must be set to CRST).
- Via menu command from the PG or via communication functions
(if the mode selector switch is set to RUN or RUN-P).
An automatic restart (warm restart) can be triggered at POWER ON if:
- The CPU was not in STOP at POWER OFF.
- The mode selector switch is set to RUN or RUN-P.
- There is no automatic hot restart or automatic cold restart parameterized for POWER ON.
- The restart (warm restart) of the CPU has not been interrupted by a power failure (independent of the startup parameterized).
- With a cold restart, data blocks created by SFCs in the main memory are deleted, while the other data blocks have the default values from the load memory.
- The process image and all timers, counters, and markers are reset to the start values in the program (load memory) regardless of whether they were set as retentive.
- The process image of the inputs is read in and the STEP 7 user program starts again at the beginning (OB 102 or OB 1).
Order of operations for cold restart:
- You can only trigger a manual cold restart from the PG.
- In the case of some S7-400 CPUs you execute a cold restart with the mode selector switch and startup mode switch (CRST/WRST) if this has been defined accordingly in the parameters with STEP 7.
After a power failure in RUN and subsequent return of power, S7-400 CPUs run through an initialization routine and then automatically execute a hot restart. After a hot restart the user program continues at that point where the processing was interrupted (timers, counters and markers are not reset and the current values are retained in DBs). The part of the user program not processed before the power failure is called the remainder cycle. The remainder cycle can also include time- and alarm-controlled program parts.
- Upon a hot restart all the data including the process image receive their last valid values.
- Program processing is continued at exactly that command where the interruption occurred.
- The outputs are not changed until the end of the current cycle.
- If the power supply is interrupted, a hot restart is only possible in buffered mode.
A hot restart is in principle only permissible if the user program has not been changed in STOP state (e.g. through loading a modified block) or if a restart (warm restart) is not necessary for other reasons.
Order of operations for hot restart:
A manual hot restart is only possible if the relevant parameters are set in the CPU and after the following reasons for the STOP:
- The mode selector switch has been switched from RUN to STOP.
- STOPs programmed by the user; STOPs after calling OBs that are not loaded.
- STOP state has been induced by the PG or a communication function.
You can trigger a manual hot restart:
- Via the mode selector switch.
- If available, the CRST/WRST switch must be set to WRST.
- Via menu command from the PG or via communication functions (if the mode selector switch is set to RUN or RUN-P).
- If manual hot restart has been parameterized in the CPU.
An automatic hot restart can be triggered at POWER ON if:
- The CPU was not in STOP or HALT at POWER OFF.
- The mode selector switch is set to RUN or RUN-P.
- Automatic hot restart has been parameterized in the CPU for POWER ON.
- If available, the CRST/WRST switch is ineffective upon automatic hot restart.