Performing A Memory Reset - Siemens SIMATIC S7-400H System Manual

Assembly of a CPU 41x–H
5.4 Mode switch
5.4.2

Performing a memory reset

Case A: You want to download a new user program to the CPU.
1. Set the switch to the STOP position.
2. Toggle the switch to MRES, and hold it in that position. In this position the mode switch
3. Then release the switch, return it to MRES within the next 3 seconds, and then release it
Case B: The STOP LED is flashing slowly at 0.5 Hz. This indicates that the CPU is
requesting a memory reset (memory reset requested by system, e.g. after a memory card
has been removed or inserted).
Toggle the switch to MRES, and then release it again.
Result: The STOP LED flashes for at least 3 seconds at 2 Hz, the memory reset is executed,
and the LED then remains lit.
Memory reset process in the CPU
During a memory reset, the following process occurs on the CPU:
● The CPU deletes the entire user program in the main memory.
● The CPU deletes the user program from the load memory. This process deletes the
● The CPU deletes all counters, bit memories, and timers, but not the time of day.
● The CPU tests its hardware.
● The CPU sets its parameters to default settings.
● If a FLASH card is inserted, the CPU copies the user program and the system
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Result: The STOP LED is lit.
acts as pushbutton.
Result: The STOP LED is off for one second, then on for one second, then again off for
one second, and then it remains lit.
again.
Result: The STOP LED flashes for at least 3 seconds at 2 Hz (memory is reset) and then
remains lit.
program from the integrated RAM and from any inserted RAM Card. The user program
elements stored on a FLASH card will not be deleted if you have expanded the load
memory with such a card.
parameters stored on the FLASH card into main memory after the memory reset.
System Manual, 03/2012, A5E00267695-11
S7-400H