am42bds6408h Meet Spansion Inc., am42bds6408h Datasheet - Page 40

• Manufacturer Part Number: am42bds6408h
• Description: Cmos 1.8 Volt-only Simultaneous Read/write, Burst Mode Flash Memory, And 8 Mbit 512 K X 16-bit Sram
• Manufacturer: Meet Spansion Inc.

SecSi Sector Protection Bit Program
Command
The SecSi Sector Protection Bit Program Command
programs the SecSi Sector Protection Bit, which pre-
vents the SecSi sector memory from being cleared. If
the SecSi Sector Protection Bit is verified as pro-
grammed without margin, the SecSi Sector Protection
Bit Program Command should be reissued to improve
program margin. Exiting the V
Protection Bit Program Command is accomplished by
writing the Read/Reset command.
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 Read/Reset
command, only while in the Persistent Sector Protec-
tion 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
(A21–A12) 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
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
38
CC
A D V A N C E
-level SecSi Sector
Am42BDS6408H
I N F O R M A T I O N
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 1uSec 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.
PPB Program Command
The PPB Program command is used to program, or
set, a given PPB. Each PPB is individually pro-
grammed (but is bulk erased with the other PPBs).
The specific sector address (A21–A12) are written at
the same time as the program command 60h with A6
= 0. If the PPB Lock Bit is set and the corresponding
PPB is set for the sector, the PPB Program command
will not execute and the command will time-out without
programming the PPB.
After programming a PPB, two additional cycles are
needed to determine whether the PPB has been pro-
grammed with margin. If the PPB has been pro-
grammed without margin, the program command
should be reissued to improve the program margin.
The PPB Program command does not follow the Em-
bedded Program algorithm.
All PPB Erase Command
The All PPB Erase command is used to erase all
PPBs in bulk. There is no means for individually eras-
ing a specific PPB. Unlike the PPB program, no spe-
cific sector address is required. However, when the
PPB erase command is written (60h) and A6 = 1, all
Sector PPBs are erased in parallel. If the PPB Lock Bit
is set the ALL PPB Erase command will not execute
and the command will time-out without erasing the
PPBs. After erasing the PPBs, two additional cycles
are needed to determine whether the PPB has been
erased with margin. If the PPBs has been erased with-
October 23, 2003