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19.4 Deleting on the Programmable Controller
Programming with STEP 7
436 Manual, 05/2010, A5E02789666-01
19.4 Deleting on the Programmable Controller
19.4.1 Erasing the Load/Work Memory and Resetting the CPU
Before downloading your user program to the S7 programmable controller, you should perform a
memory reset on the CPU to ensure that no "old" blocks are still on the CPU.
Requirement for Memory Reset
The CPU must be in STOP mode to perform a memory reset (mode selector set to STOP, or to
RUN-P and change the mode to STOP using the menu command PLC > Diagnostics/Settings >
Operating Mode).
Performing a Memory Reset on an S7 CPU
When a memory reset is performed on an S7 CPU, the following happens:
• The CPU is reset.
• All user data are deleted (blocks and system data blocks (SDB) with the exception of the MPI
parameters).
• The CPU interrupts all existing connections.
• If data are present on an EPROM (memory card or integrated EPROM), the CPU copies the
EPROM contents back to the RAM area of the memory following the memory reset.
The contents of the diagnostic buffer and the MPI parameters are retained.
Performing a Memory Reset on M7 CPUs/FMs
When a memory reset is performed on an M7 CPU/FM, the following happens:
• The original state is restored.
• The system data blocks (SDB) with the exception of the MPI parameters are deleted.
• The CPU/FM breaks off all existing connections. User programs are retained and will continue
running after you switch the CPU from STOP to RUN.
With the "memory reset" function you can restore the original state of the M7 CPU or FM following
serious errors by deleting the current system data blocks (SDB) from the work memory and
reloading the SDBs in the read-only memory. In some cases, a warm restart of the operating
system will be required. To do this, you clear the M7 using the mode selector (switch to MRES
position). A reset using the mode selector on SIMATIC M7 CPUs or FMs is only possible if the
RMOS32 operating system is used on the CPU/FM.