If your goal is to , and you either have the original program (as a backup) or do not need to preserve what is on the PLC, the officially supported solution is to erase the MMC entirely.
The S7-300 PLC has a built-in feature to reset the password using the device's front panel. Here's how:
Look for the line containing the keyword KNOW_HOW_PROTECT near the top of the block definition. Delete this exact line.
Wait for the to flash slowly, then release the switch.
an S7-300 MMC card to prevent this issue in the future.
SIEMENS Simatic S7-300 (pre-2009 versions) Default Password, How To
Elias sat back, the rhythmic hum of the mill returning. The first thing he did? He didn't just write the password down—he updated the CPU protection levels and made sure the new code was stored in the company’s secure digital vault. No more digital archeology for him.
This is the most common request. An integrator locks a function block (using "Know-How Protection" in Step 7) to protect proprietary algorithms. If the source is lost, the logic inside the block cannot be viewed or edited.
: For older, pre-2009 versions of the S7-300, the default password was sometimes set to "Basisk" .
If you have physical access to the PLC and the original programming device (PG), you have options. Try these before attempting any third-party hacks.
Remove the Micro Memory Card (MMC) if you want to wipe external storage entirely.
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