The following steps should be followed to issue a Chip Erase.
- Enter the CHIPERASE KEY by using
the KEY instruction. See Table 2 for the CHIPERASE signature.
- Optional: Read the Chip
Erase bit in the AS Key Status register (CHIPERASE in UPDI.ASI_KEY_STATUS) to
see that the KEY is successfully activated.
- Write the Reset signature into
the UPDI.ASI_RESET_REQ register. This will issue a System Reset.
- Write 0x00 to the ASI Reset
Request register (UPDI.ASI_RESET_REQ) to clear the System Reset.
- Read the Lock Status bit in the
ASI System Status register (LOCKSTATUS in UPDI.ASI_SYS_STATUS).
- Chip Erase is done when
LOCKSTATUS == 0 in UPDI.ASI_SYS_STATUS. If LOCKSTATUS == 1, go to point 5
again.
After a successful Chip Erase, the Lockbits will be cleared, and the UPDI
will have full access to the system. Until Lockbits are cleared, the UPDI cannot access
the system bus, and only CS-space operations can be performed. See User Row Programming.
During Chip Erase, the
BOD is forced ON (ACTIVE=0x1 in BOD.CTRLA), and uses the BOD Level from the BOD
Configuration fuse (LVL in BOD.CTRLB = LVL in FUSE.BODCFG). If the supply voltage
VDD is below that threshold level, the device is unserviceable until VDD
is increased adequately.