AM29BDS128HD8VFI AMD [Advanced Micro Devices], AM29BDS128HD8VFI Datasheet - Page 43

• Manufacturer Part Number: AM29BDS128HD8VFI
• Description: 128 or 64 Megabit (8 M or 4 M x 16-Bit) CMOS 1.8 Volt-only Simultaneous Read/Write, Burst Mode Flash Memory
• Manufacturer: AMD [Advanced Micro Devices]

tection Mode Locking Bit is programmed. If not, the
system must repeat this program sequence from the
fourth cycle of “PL/68h”. Exiting the Persistent Protec-
tion Mode Locking Bit Program command is accom-
plished by writing the SecSi Sector Exit command or
Reset command.
SecSi Sector Protection Bit Program
Command
To protect the SecSi Sector, write the SecSi Sector
Protect command sequence while in the SecSi Sector
mode. After issuing “OPBP/48h” at the fourth bus cy-
cle, the device requires a time out period of approxi-
mately 150 µs to protect the SecSi Sector. Then, by
writing “OPBP/48” at the fifth bus cycle, the device out-
puts verify data at DQ0. If DQ0 = 1, then the SecSi
Sector is protected. If not, then the system must re-
peat this program sequence from the fourth cycle of
“OPBP/48h”.
PPB Lock Bit Set Command
The PPB Lock Bit Set command is used to set the
PPB Lock bit if it is cleared either at reset or if the
Password Unlock command was successfully exe-
cuted. There is no PPB Lock Bit Clear command.
Once the PPB Lock Bit is set, it cannot be cleared un-
less the device is taken through a power-on clear or
the Password Unlock command is executed. Upon set-
ting the PPB Lock Bit, the PPBs are latched into the
DYBs. If the Password Mode Locking Bit is set, the
PPB Lock Bit status is reflected as set, even after a
power-on reset cycle. Exiting the PPB Lock Bit Set
command is accomplished by writing the SecSi Sector
Exit command, only while in the Persistent Sector Pro-
tection Mode.
DYB Write Command
The DYB Write command is used to set or clear a DYB
for a given sector. The high order address bits
(Amax–A11) are issued at the same time as the code
01h or 00h on DQ7-DQ0. All other DQ data bus pins
are ignored during the data write cycle. The DYBs are
modifiable at any time, regardless of the state of the
PPB or PPB Lock Bit. The DYBs are cleared at
power-up or hardware reset. Exiting the DYB Write
May 10, 2006 27024B3
Am29BDS128H/Am29BDS640H
D A T A
S H E E T
command is accomplished by writing the Read/Reset
command.
Password Unlock Command
The Password Unlock command is used to clear the
PPB Lock Bit so that the PPBs can be unlocked for
modification, thereby allowing the PPBs to become ac-
cessible for modification. The exact password must be
entered in order for the unlocking function to occur.
This command cannot be issued any faster than 2 µs
at a time to prevent a hacker from running through the
all 64-bit combinations in an attempt to correctly match
a password. If the command is issued before the 2 µs
execution window for each portion of the unlock, the
command will be ignored.
The Password Unlock function is accomplished by
writing Password Unlock command and data to the de-
vice to perform the clearing of the PPB Lock Bit. The
password is 64 bits long, so the user must write the
Password Unlock command 4 times. A1 and A0 are
used for matching. Writing the Password Unlock com-
mand is not address order specific. The lower address
A1–A0= 00, the next Password Unlock command is to
A1–A0= 01, then to A1–A0= 10, and finally to A1–A0=
11.
Once the Password Unlock command is entered for all
four words, the RDY pin goes LOW indicating that the
device is busy. Approximately 1 µs is required for each
portion of the unlock. Once the first portion of the
password unlock completes (RDY is not driven and
DQ6 does not toggle when read), the Password Un-
lock command is issued again, only this time with the
next part of the password. Four Password Unlock com-
mands are required to successfully clear the PPB
Lock Bit. As with the first Password Unlock command,
the RDY signal goes LOW and reading the device re-
sults in the DQ6 pin toggling on successive read oper-
ations until complete. It is the responsibility of the
microprocessor to keep track of the number of Pass-
word Unlock commands, the order, and when to read
the PPB Lock bit to confirm successful password un-
lock. In order to relock the device into the Password
Mode, the PPB Lock Bit Set command can be re-is-
sued. Exiting the Password Unlock Command is ac-
complished by writing SecSi Sector Exit command.
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