The PMBus 1.5 standard command PASSKEY provides a customer with the ability to lock access to EXT_WRITE_PROTECTION with a User Programmed up to 32-bit passkey[KJ1] . The PASSKEY will accept fewer or more bytes on a write without NACKing.

Return to Supported PMBus Commands.

Writing a non-zero value using PASSKEY will lock write access to EXT_WRITE_PROTECT (and STORE_USER_ALL if SNVML (EXT_WP[0]) is set) only after sending a STORE_USER_ALL command and performing a POWER_ON_RESET, or sending the PMBus command RESTORE_USER_ALL.

As a user option the NVM_CHECKSUM is read back as the next two bytes after the PASSKEY data.

When PASSKEY = 0000h, EXT_WRITE_PROTECT is unlocked and writable unless write protected by WRITE_PROTECT or EXT_WRITE_PROTECT . Non-Volatile memory is Unlocked. STORE commands function normally unless write protected by WRITE_PROTECT or EXT_WRITE_PROTECT . A READ on PASSKEY that has not yet been written will return 0000h. A WRITE on PASSKEY will set PASSKEY to be stored to NVM via STORE_USER_ALL.

When PASSKEY =! 0000h, Non-Volatile memory is locked. STORE_USER_ALL and EXT_WRITE_PROTECT is NACKED as “UNSUPPORTED or INVALID DATA”

A READ on PASSKEY will report a value of:

• 10h if no invalid attempts 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

If a WRITE on PASSKEY does not match the value of PASSKEY in PASSKEY at Power On Reset or RESTORE_USER_ALL, the PASSKEY invalid access attempt counter is incremented. If the Counter reaches 3, all further WRITE attempts are considered invalid and the device will NACK and set IVD_DATA bit in STATUS_CML

If the WRITE data matches the Passkey used to PASSKEY access and less than 3 invalid attempts have been made, PASSKEY is allowed to be overwritten with a new PASSKEY value, including 0000h and the Invalid Attempts counter is reset to 0.