PASSKEY is shown in Figure 8-35 and described in Table 8-44.

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Write Transaction: Write Block (1 byte)
Read Transaction: Read Block (3 byte)
Data Format: Unsigned Binary (1 byte)
NVM Back-up: EEPROM
Updates: On-the-fly Passkey provides a user the ability to lock access to (15h) STORE_USER_ALL and (10h) WRITE_PROTECT with a user programmed 8-bit value. On reads, PASSKEY will return 3 bytes with the upper two bytes mirroring the NVM_CHECKSUM and the lowest byte reflecting the current PASSKEY status. When unlocked, the lowest byte of PASSKEY reads back 00h. When PASSKEY is unlocked after Power On Reset or RESTORE_USER_ALL:
Non-volatile memory is unlocked. WRITE_PROTECT is unlocked and writeable. STORE_USER_ALL functions normally. A READ on PASSKEY will return 00h. WRITE will update PASSKEY, but the value must be stored to NVM via STORE_USER_ALL to take effect. When PASSKEY is locked after Power On Reset or RESTORE_USER_ALL:
Non-volatile memory is locked. STORE_USER_ALL and WRITE_PROTECT shall be NACKED as "UNSUPPORTED or INVALID DATA."
A READ on PASSKEY will report a value of:
– 10h if no invalid attemps have been made to unlock PASSKEY
– 11h if One invalid attempt has been made to unlock PASSKEY
– 12h if Two invalid attempts have been made to unlock PASSKEY
– 1Fh if Three or more invalid attempts have been made to unlock PASSKEY. The invalid access attempt counter will be reset only after a Power On Reset. After PASSKEY is set, a RESTORE_USER_ALL or WRITE to PASSKEY with incorrect value will increment the counter as outlined above. After 3 incorrect attempts, further WRITE attempts will be ACKed, with no STATUS bits set, but the PASSKEY shall remain locked even if the matching PASSKEY value is written. If the WRITE data matches the PASSKEY and less than three invalid attempts have been made, PASSKEY will now read back the current PASSKEY value, and can be overwritten with a new value (including 00h which will leave the device unlocked).The invalid attempt counter will be reset to 0. STORE_USER_ALL and WRITE_PROTECT will allow write access. A STORE_USER_ALL command must be issued for the new PASSKEY value to take effect.