Entry type: FAQ Entry ID: 109782017, Entry date: 10/12/2020

Why does the message "16# 4546 STOP caused by CPU memory management” appear in the diagnostics buffer with an S7-300 CPU?

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You get this message in the diagnostics buffer of STEP 7 (TIA Portal) if the S7-300 CPU recognizes an access error to the MMC.

If there is an access error to the MMC (Micro Memory Card) the following diagnostic analysis is displayed in the diagnostics buffer of the S7-300 CPU:

48 of 50; Event ID: 16# 4546
STOP caused by CPU memory management
Previous operating mode: RUN
Request operating mode: STOP (internal)
Internal error
Incoming event
07.11.2017 05:48:48.010

49 of 50; Event ID: 16# 6523
Request for overall reset due to MMC access error
Not user-relevant (Z2): 8020  (Z3): 1410
Operating mode: RUN
Internal error
Incoming event
07.11.2017 05:48:48.010

The following list shows possible causes for this:

  • Strong vibration (for example, the MMC contact is no longer snug)
  • MMC card is defective
  • MMC card holder is defective (CPU replacement required)
  • Bit dumper/bit error in the memory (EMC)
  • Is the MMC an original Siemens Micro Memory Card?
    Information about this is available in our entry entitled Which memory cards can you use with an S7-300 CPU?.
  • The maximum number of write-read cycles has been reached.
    Note that the MMC supports only a limited number of write cycles. According to the manufacturer, 100,000 write cycles are possible. If an access to the MMC is executed cyclically, the maximum write-read cycles are reached within shortest time. For example, the SFC84 that saves data areas in the load memory. Use system functions that access the MMC (load memory) only for acyclic storage of important configuration data. 

We recommend that you always upgrade to the latest firmware version of the S7-300 CPU. Information and the download are available here: Firmware Updates.

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