36.3.8 Enabling of Key Protected Interfaces

The access to some internal interfaces and features is protected by the UPDI key mechanism. To activate a key, the correct key data must be transmitted by using the KEY instruction, as described in 36.3.3.8 KEY - Set Activation Key or Send System Information Block. Table 36-4 describes the available keys and the condition required for starting the operation after the key has been loaded.

Table 36-4. Key Activation Overview
Key Name	Description	Requirements for Operation	Conditions for Key Invalidation
Chip Erase	Start NVM chip erase. Clear lock bits.	—	UPDI Disable/UPDI Reset
NVMPROG	Activate NVM programming	Lock bits cleared. ASI_SYS_STATUS.PROGSTART set.	Programming done/UPDI Reset
USERROW-Write	Program the user row on the locked device	ASI_SYS_STATUS.UROWSTART set	Write to key Status bit/UPDI Reset

Table 36-5 gives an overview of the available key signatures that must be shifted in to activate the interfaces.

Table 36-5. Key Activation Signatures
Key Name	Key Signature (LSB Written First)	Size
Chip Erase	0x4E564D4572617365	64 bits
NVMPROG	0x4E564D50726F6720	64 bits
USERROW-Write	0x4E564D5573267465	64 bits