DS1852

4 of 25

DEVICE OPERATION

Security

To prevent accidental overwrites of key device data, a data lockout feature is incorporated. A 32-bit

password provides access to the “manufacturer” memory locations. These locations are in addition to the

unprotected “user” memory locations:

1) User—This is the default state after power-up; it allows read access to standard IEEE identity table

and standard monitoring and status functions.

2) Manufacturer Level 1—This allows access to customer data table and some selected setups (password

1).

3) Manufacturer Level 2—This allows access to all memory, settings, and features (password 2).

The level 1 password is located in Table 03h EEPROM (bytes D3h to D6h) and may be changed by

gaining access through the level 2 password.

The level 2 password is set in protected EEPROM and is programmed during factory test.

During power-up, the 32-bit password entry (addresses 7Bh to 7Eh) is set to all 1s. This is the value that

is compared to the level 1 password entry in Table 03h to grant level 1 access. Therefore, the level 1

password should not be set to all 1s or the user will gain level 1 access after each power-on.

By default, both passwords are factory preset to 00h.

To gain access to a security level, a 4-byte password is written into Table 00h, bytes 7Bh to 7Eh. If the

written data matches one of the passwords, that corresponding level of access is granted until the

password entry is changed or the power is cycled. Entering the level 2 password allows access to both

the level 1 data and the level 2 data. The 4-byte password is write-only.