35.3.7 Enabling of Key Protected Interfaces

The UPDI key mechanism protects the access to some internal interfaces and features. To activate a key, the correct key data must be transmitted by using the KEY instruction, as described in the KEY - Set Activation Key or Send System Information Block section. Table 35-5 describes the available keys and the condition required when doing the operation with the key active.

Table 35-5. 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.NVMPROG set	Programming done/UPDI Reset
USERROW-Write	Program the user row on the locked device	Lock bits set. ASI_SYS_STATUS.UROWPROG set	Write to key Status bit/UPDI Reset

Table 35-6 gives an overview of the available key signatures that must be shifted in to activate the interfaces.

Table 35-6. 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