Operating Sequence For Memory Reset - Siemens SIMATIC S7-400H System Manual

5.6

Operating sequence for 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. This selector switch position has
3. Release the switch, return it to MRES within the next three seconds, and then release it
Case B: The STOP LED flashing slowly at 0.5 Hz indicates that the CPU is requesting a
memory reset (system memory reset request, after a memory card has been removed or
inserted for example).
Toggle the switch to MRES, and then release it again.
Result: The STOP LED flashes for at least 3 seconds at 2 Hz (CPU memory reset is being
executed), and then is lit steadily.
Sequence of a CPU memory reset
CPU memory reset sequence:
● The CPU deletes the entire user program from the RAM.
● The CPU deletes the user program from the load memory. This process deletes the
● The CPU resets all counters. memory markers and timers, but not the time of day.
● The CPU tests its hardware.
● The CPU sets its parameters to default values.
● When a FLASH Card is inserted, the CPU continues after its memory reset by copying
S7-400H
System Manual, 09/2007, A5E00267695-03
Result: The STOP LED lights.
a pushbutton action contact.
Result: The STOP LED is unlit for a second, lit for a second, unlit for a second and then
remains lit steadily.
again.
Result: The STOP LED flashes for at least 3 seconds at 2 Hz (CPU memory reset is
being executed), and then is lit steadily.
program from the on-board RAM and from any RAM Card. The user program elements
stored on Flash card will not be deleted if you have expanded the load memory with such
a card.
the user program and the system parameters from the FLASH card to RAM.
Installation of a CPU 41x–H
5.6 Operating sequence for memory reset
51