Micrel, Inc.
MIC3001
August 2004
37
M9999-082404-A
Figure 25. Four-Byte Page_White Protocol
Acknowledge Polling
The MIC3001’s non-volatile memory cannot be accessed
during the internal write process. To allow for maximum
speed bulk writes, the MIC3001 supports acknowledge
polling. The MIC3001 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
MIC3001, specifically the non-volatile memory, look-up
tables, and registers at serial addresses A4h and A6h. A
four-byte field, OEMPWSET, at serial address A6h 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 7Bh at serial address
A2h. Therefore, this byte must be written last! A four-
byte burst-write sequence to address 78h 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 A2h. This field is
therefore always visible to the host system. OEMPW is
compared to the four-byte OEMPWSET field at serial
address A6h. If the two fields match, access is allowed to
the OEM areas of the MIC3001 non-volatile memory at
serial addresses A4h and A6h. If OEMPWSET is all
zeroes, no password security will exist. The value in
OEMPW will be ignored. This helps prevent a deliberately
unsecured MIC3001 from being inadvertently locked.
Once a valid password is entered, the MIC3001 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 (00000000h), the MIC3001 will
remain unlocked regardless of the contents of the OEMPW
field. This is the factory default security setting.
NOTE: 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
MIC3001, specifically the non-volatile memory at serial
addresses A0h and A2h. A one-byte field, USRPWSET at
serial address A2h is used for setting the USER password.
USRPWSET is compared to the USRPW field at serial
address A2h. If the two fields match, access is allowed to
the USER areas of the MIC3001 non-volatile memory at
serial addresses A0h and A2h. 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: 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. If a valid
OEM password is in place, the user password will have no
effect.