8.11 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). Locking protects Flash (all Boot Code, Application Code, and Application Data sections), SRAM, and the EEPROM, including the FUSE data, thereby preventing application data or code from being read through the debugger interface. Regular memory access from within the application remains enabled.

The CPU and UPDI can read the Lock Key, but it can be programmed or cleared only by UPDI. The device is locked by writing an invalid 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
SIGROW	Yes	No	Yes	No
BOOTROW	Yes⁽²⁾	Yes⁽²⁾	Yes	Yes
USERROW	Yes	Yes	Yes	Yes
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
SIGROW	Yes	No	No	No
BOOTROW	Yes⁽²⁾	Yes⁽²⁾	No	No
USERROW	Yes	Yes	No	Yes⁽³⁾
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 are invalid. Therefore, any attempt at code validation through UPDI will fail for these memory sections.
Write and read operations are possible only from the Boot section.
In 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 are retained.