Some MCUs (like the Motorola 9S12 in automotive ECUs) require a 12V pulse on a specific pin (MODB or BKGD) to enter "Unsecure" mode. This erases the lock flag.
| Cause | Description | Probability | | :--- | :--- | :--- | | | The chip's RDP bits are set to Level 1. Normal flash tools cannot unlock this without a full erase. | High (60%) | | 2. Incomplete Previous Flash | A power loss or USB disconnect during flashing left the lock flag in an indeterminate state. | Medium (20%) | | 3. Wrong Unlock Sequence | The debug interface (JTAG/SWD) tried to write without sending the correct unlock key. | Medium (10%) | | 4. Hardware Write-Protect Pin | Some MCUs have a physical pin (WP) held high. If strapped to VCC, software cannot unlock. | Low (5%) | | 5. Option Byte Corruption | The configuration bytes that control flash locking have been corrupted by ESD or voltage spike. | Low (3%) | | 6. Clone/Debugger Issue | Cheap Chinese ST-Link clones often fail to send the unlock command sequence properly. | Low (2%) | flashing lock flag is locked
The error message "FAILED (remote: 'Flashing Lock Flag is locked. Please unlock it first!')" Some MCUs (like the Motorola 9S12 in automotive
For extreme cases, desolder the flash chip (often a SOIC-8 or WSON-8) and use a dedicated external programmer (like TL866II Plus) to manually reset all lock bits. Normal flash tools cannot unlock this without a full erase