8.9 LOCK - Memory Sections Access Protection

The device can be locked so that the memories cannot be read using the Unified Program and Debug Interface (UPDI). The locking protects the Flash (all Boot Code, Application Code, and Application Data sections), SRAM, and the EEPROM including the FUSE data, which prevents the reading of application data or code using the debugger interface. Regular memory access from within the application is still enabled.

The CPU and UPDI can read the Lock Key, but it can only be programmed or cleared by the UPDI. The device is locked by writing a non-valid key to the Lock Key (LOCK.KEY) register.

Table 8-5. Memory Access Unlocked (LOCK.KEY Valid Key)⁽¹⁾
Memory Section	CPU Access		UPDI Access
Memory Section	Read	Write	Read	Write
Flash	Yes	Yes	Yes	Yes
SRAM	Yes	Yes	Yes	Yes
EEPROM	Yes	Yes	Yes	Yes
USERROW	Yes	Yes	Yes	Yes
SIGROW	Yes	No	Yes	No
FUSE	Yes	No	Yes	Yes
LOCK	Yes	No	Yes	Yes
Registers	Yes	Yes	Yes	Yes

Table 8-6. Memory Access Locked (LOCK.KEY Invalid Key)⁽¹⁾
Memory Section	CPU Access		UPDI Access
Memory Section	Read	Write	Read	Write
Flash	Yes	Yes	No	No
SRAM	Yes	Yes	No	No
EEPROM	Yes	Yes	No	No
USERROW	Yes	Yes	No	Yes⁽²⁾
SIGROW	Yes	No	No	No
FUSE	Yes	No	No	No
LOCK	Yes	No	No	No
Registers	Yes	Yes	No	No

Note:

Read operations marked No in the tables may appear successful, but the data is invalid. Hence, any attempt of code validation through the UPDI will fail on these memory sections.
In the Locked mode, the USERROW can be written using the Fuse Write command, but the current USERROW values cannot be read.

Important: The only way to unlock a device is to perform a CHIPERASE. No application data is retained.