MIC3002 Datasheet, PDF (39/65 Pages) Micrel Semiconductor – FOM Management IC with Internal Calibr ation

Micrel, Inc.
MIC3002
Figure 24. Four-Byte Page White Protocol
Acknowledge Polling
The MIC3002’s non-volatile memory cannot be accessed
during the internal write process. To allow for maximum
speed bulk writes, the MIC3002 supports acknowledge
polling. The MIC3002 will not acknowledge serial bus
transactions while internal writes are in progress. The host
may therefore monitor for the end of the write process by
periodically checking for an acknowledgement.
Write Protection and Data Security
OEM Password
A password is required to access the OEM areas of the
MIC3002, specifically the non-volatile memory, look-up
tables, and registers at serial addresses A4_h and A6_h. A four-
byte field, OEMPWSET, at serial address A6_h is used for
setting the OEM password. The OEM password is set by
writing OEMPWSET with the new value. The password
comparison is performed following the write to the MSB of
the OEMPW, address 7B_h (or 7E_h) at serial address A2_h.
Therefore, this byte must be written last. A four-byte burst-
write sequence to address 78_h (or 7B_h) may be used as this
will result in the MSB being written last. The new password
will not take effect until after a power-on reset occurs or a
warm reset is performed using the RST bit in OEMCFG0.
This allows the new password to be verified before it takes
effect.
The corresponding four-byte field for password entry,
OEMPW, is located at serial address A2_h. This field is
therefore always visible to the host system. OEMPW is
compared to the four-byte OEMPWSET field at serial
address A6_h. If the two fields match, access is allowed to the
OEM areas of the MIC3002 non-volatile memory at serial
addresses A4_h and A6_h. If OEMPWSET is all zeroes, no
password security will exist. The value in OEMPW will be
ignored. This helps prevent a deliberately unsecured
MIC3002 from being inadvertently locked. Once a valid
password is entered, the MIC3002 OEM areas will be
accessible. The OEM areas may be re-secured by writing an
incorrect password value at OEMPW, e.g., all zeroes. In all
cases, OEMPW must be written LSB first through MSB last.
The OEM areas will be inaccessible following the final write
operation to OEMPW’s LSB. The OEMPW field is reset to all
zeros at power on. Any values written to these locations will be
readable by the host regardless of the locked/unlocked status
of the device. If OEMPWSET is set to zero (00000000_h), the
MIC3002 will remain unlocked regardless of the contents of the
OEMPW field. This is the factory default security setting.
Note that a valid OEM password allows access to the OEM
and user areas of the chip, i.e., the entire memory map,
regardless of any user password that may be in place. Once
the OEM areas are locked, the user password can provide
access and write protection for the user areas.
User Password
A password is required to access the USER areas of the
MIC3002, specifically, the non-volatile memory at serial
addresses A0_h and A2_h. A one-byte field, USRPWSET at serial
address A2_h is used for setting the USER password.
USRPWSET is compared to the USRPW field at serial address
A2_h. If the two fields match, access is allowed to the USER
areas of the MIC3002 non-volatile memory at serial addresses
A0_h and A2_h. The USER password is set by writing
USRPWSET with the new value. The new password will not
take effect until after a power-on reset occurs or a warm reset
is performed using the RST bit in OEMCFG0. This allows the
new password to be verified before it takes effect.
Note also that a valid OEM password allows access to the
OEM and user areas of the chip, i.e., the entire memory map,
regardless of any user password that may be in place. Once
the OEM areas are locked, the user password can then provide
access and write protection for the user areas. If a valid OEM
password is in place, the user password will have no effect.
July 2007
39
M9999-073107-B
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