34.3.7 Enabling of KEY Protected Interfaces

Access to some internal interfaces and features are 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 KEY instruction. Table 34-5 describes the available KEYs, and the condition required when doing the operation with the KEY active. There is no requirement when shifting in the KEY, but you would, for instance, normally run a Chip Erase before enabling the NVMPROG KEY to unlock the device for debugging. But if the NVMPROGKEY is shifted in first, it will not be reset by shifting in the Chip Erase KEY afterwards.

Table 34-5. KEY Activation Overview
KEY NameDescriptionRequirements for OperationReset
Chip EraseStart NVM Chip erase. Clear LockbitsNoneUPDI Disable/UPDI Reset
NVMPROGActivate NVM ProgrammingLockbits Cleared. ASI_SYS_STATUS.NVMPROG set.Programming Done/UPDI Reset
USERROW-WriteProgram User Row on Locked partLockbits Set. ASI_SYS_STATUS.UROWPROG set.Write to KEY status bit/UPDI Reset

Table 34-6 gives an overview of the available KEY signatures that must be shifted in to activate the interfaces.

Table 34-6. KEY Activation Signatures
KEY NameKEY Signature (LSB Written First)Size
Chip Erase0x4E564D457261736564 bits
NVMPROG0x4E564D50726F672064 bits
USERROW-Write0x4E564D557326746564 bits