am42bds6408h Meet Spansion Inc., am42bds6408h Datasheet - Page 39

• 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.

are ignored. Another Erase Suspend command can be
written after the chip has resumed erasing.
Password Program Command
The Password Program Command permits program-
ming the password that is used as part of the hard-
ware protection scheme. The actual password is
64-bits long. 4 Password Program commands are re-
quired to program the password. The user must enter
the unlock cycle, password program command (38h)
and the program address/data for each portion of the
password when programming. There are no provisions
for entering the 2-cycle unlock cycle, the password
program command, and all the password data. There
is no special addressing order required for program-
ming the password. Also, when the password is under-
going programming, Simultaneous Operation is
disabled. Read operations to any memory location will
return the programming status. Once programming is
complete, the user must issue a Read/Reset com-
mand to return the device to normal operation. Once
the Password is written and verified, the Password
Mode Locking Bit must be set in order to prevent verifi-
cation. The Password Program Command is only ca-
pable of programming “0”s. Programming a “1” after a
cell is programmed as a “0” results in a time-out by the
Embedded Program Algorithm™ with the cell remain-
ing as a “0”. The password is all F’s when shipped
October 23, 2003
Notes:
1. See Table 16 for erase command sequence.
2. See the section on DQ3 for information on the sector
erase timer.
No
Figure 5. Erase Operation
Command Sequence
Erasure Completed
Write Erase
from System
Data = FFh?
Data Poll
START
Yes
A D V A N C E
Embedded
Erase
algorithm
in progress
Am42BDS6408H
I N F O R M A T I O N
from the factory. All 64-bit password combinations are
valid as a password.
Password Verify Command
The Password Verify Command is used to verify the
Password. The Password is verifiable only when the
Password Mode Locking Bit is not programmed. If the
Password Mode Locking Bit is programmed and the
user attempts to verify the Password, the device will al-
ways drive all F’s onto the DQ data bus.
Also, the device will not operate in Simultaneous Oper-
ation when the Password Verify command is executed.
Only the password is returned regardless of the bank
address. The lower two address bits (A1–A0) are valid
during the Password Verify. Writing the Read/Reset
command returns the device back to normal operation.
Password Protection Mode Locking Bit
Program Command
The Password Protection Mode Locking Bit Program
Command programs the Password Protection Mode
Locking Bit, which prevents further verifies or updates
to the Password. When the Password Protection Mode
Locking Bit is undergoing programming, Simultaneous
Operation is disabled. Once programmed, the Pass-
word Protection Mode Locking Bit cannot be erased! If
the Password Protection Mode Locking Bit is verified
as program without margin, the Password Protection
Mode Locking Bit Program command can be executed
to improve the program margin. Once the Password
Protection Mode Locking Bit is programmed, the Per-
sistent Sector Protection Locking Bit program circuitry
is disabled, thereby forcing the device to remain in the
Password Protection mode. Exiting the Mode Locking
Bit Program command is accomplished by writing the
Read/Reset command.
Persistent Sector Protection Mode
Locking Bit Program Command
The Persistent Sector Protection Mode Locking Bit
Program Command programs the Persistent Sector
Protection Mode Locking Bit, which prevents the Pass-
word Mode Locking Bit from ever being programmed.
If the Persistent Sector Protection Mode Locking Bit is
verified as programmed without margin, the Persistent
Sector Protection Mode Locking Bit Program Com-
mand should be reissued to improve program margin.
By disabling the program circuitry of the Password
Mode Locking Bit, the device is forced to remain in the
Persistent Sector Protection mode of operation, once
this bit is set. Exiting the Persistent Protection Mode
Locking Bit Program command is accomplished by
writing the Read/Reset command. When the Persis-
tent Sector Protection Mode Locking Bit is undergoing
programming, Simultaneous Operation is disabled.
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