Automation and Drives - SCE
Retentivity
Your CPU 31xC has retentive memory. Retentivity is implemented on the MMC and on the CPU. Due to this retentivity, the contents of the retentive memory are retained even after the mains supply has been switched off and the CPU has been restarted (warm restart).
Load memory
You program in the load memory (MMC) is always retentive. During loading, it is stored on the MMC, is
Work memory (RAM)
Your data in the work memory are backed up on the MMC in the event that the mains supply is switched off. The contents of data blocks are therefore always retained.
System memory
With regard to clock memories, timers and counters, you configure (properties of the CPU, Retentivity tab) which parts are to be retentive and which are to be initialized with "0" when the system is restarted (warm restart).
The diagnostic buffer, MPI address (and baud rate) as well as the runtime meter are generally stored in the retentive memory area on the CPU. The retentive area for the MPI address and the baud rate ensure that your CPU is still able to communicate after a power failure, a complete memory reset or loss of the communication parameters (because the MMC was removed, or the communication parameters were deleted).
Retention of the memory objects
The following table shows which memory objects are retained when transitions between operating modes occur.
Memory Object | Operating Mode Transition | |
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| STOP Æ |
| PowerOn/PowerOff | |
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| RUN |
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| X |
User Program/User Data (load memory) | X | |
Actual values of the DBs | X | X |
Flags, timers and counters configured as | X | X |
retentive |
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Diagnostic buffer, hours run meter | X | X |
MPI address, baud rate | X | X |
Memory
Reset
X
-
-
X
X
X = retentive; - = not retentive
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Foreword | Notes | Hardware configuration | STEP 7 program | Testing |
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T I A Training Document |
| Page 10 of 25 |
| Module | |
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| A5 | |
Issue date: 02/2008 |
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| Programming the CPU | ||
