Switch the power back on while continuing to hold the switch in MRES.
Read/Write protection (complete lockout without the password). Method 1: The MMC Card Reader Method (Most Effective) unlock s7300 plc password
When an engineer uploads a project from the PLC to the engineering station (Step 7), the password is not transmitted in plaintext, but the handshake involves sending a hash. Switch the power back on while continuing to
| Method | Data Retention | Success Rate | Complexity | Requirements | | :--- | :--- | :--- | :--- | :--- | | | Complete | 100% (if file exists) | Low | Original STEP 7 / TIA project | | S7_JOB.S7S Reset File | Complete loss | Very high | Low | Empty Micro SD card | | MMC Card Tools (Third‑Party) | Preserves data | Moderate | Medium | Standard SD card reader, special software | | Password Decryption (Brute Force) | Preserves data | Very low (weak passwords only) | Very high | TIA Portal, Wireshark, S7 client | | Cross‑CPU Passive Format | Complete loss | Very high | Low | Another S7‑300 CPU (different model) | | Method | Data Retention | Success Rate
depends heavily on your end goal: whether you need to or simply reset the hardware to reuse it. Because these PLCs are legacy devices, several "workaround" methods exist, but most come with the caveat of permanent data loss. 1. The Strategy of Hardware Reset (Data Loss)
On older S7-300 units, security relied heavily on the physical MMC (Micro Memory Card). Modern iterations integrate deeply with TIA Portal firmware, making simple hardware exploits much more difficult. Method 1: The Official Factory Reset (Wipe and Restore)