What should you do upon display of the error message 33:8580 "MMC defective"
The error message concerned indicates that the MMC is no longer recognized/accepted by the SIMATIC CPU. This is the case when the SIMATIC IDs have been overwritten, for example through using the MMC in a non-SIMATIC application, or the MMC has been formatted in a third-party device. Unfortunately it is not possible to restore the internal structure of the MMC for renewed use in SIMATIC S7-300 CPUs.
See Entry ID 21829579 for which SIMATIC devices you can use to read from or write to S7-300 MMCs. More information on handling the MMC is available in the manual "S7-300, CPU 31xC and CPU 31x: Installation Instructions" in Entry ID 13008499.