SST38VF6401B Datasheet, PDF (15/58 Pages) Microchip Technology – 64 Mbit (x16) Advanced Multi-Purpose Flash Plus

SST38VF6401B / SST38VF6402B / SST38VF6403B / SST38VF6404B
4.16.2 PASSWORD MODE (DQ₂, DQ₁ = 0,1)
In the Password Mode, the Global Lock Bit is set to ‘0’
by the Set Global Lock Bit command, a power-down
power-up sequence, or a hardware reset (RST# pin =
0). Select the Password only mode by programming
PSR bit DQ₂ = 0 and DQ₁ = 1. Note that when the PSR
Program command is issued in Password mode, the
Global Lock bit is automatically set to ‘0’.
In contrast to the Pass-Through Mode, in the Password
mode, the only way to clear the Global Lock Bit to ‘1’ is
to submit the correct 64-bit password using the Submit
Password command in Password Commands Mode.
The words of the password can be submitted in any
order as long as each 16 bit section of the password is
matched with its correct address. After the entire 64 bit
password is submitted, the device takes approximately
1 µs to verify the password. A subsequent Submit
Password command cannot be issued until this verifi-
cation time has elapsed.
The 64-bit password must be chosen by the user
before programming the DQ₂ and DQ₁ OTP bits of the
PSR to choose Password Mode. The default 64 bit
password on the device from the factory is
FFFFFFFFFFFFFFFFh.
Enter the Password Commands mode by issuing the
Password Commands Entry command. Then, use the
Password Program command to program the desired
password. Use caution when programming the pass-
word because there is no method to reset the password
to FFFFFFFFFFFFFFFFh. Once a password bit has
been set to ‘0’, it cannot be changed back to ‘1’. See
Table 5-2 for further details about Password-related
commands.
The password can be read using the Password Read
command to verify the desired password has been pro-
grammed. Microchip recommends testing the pass-
word before permanently choosing Password Mode.
To test the password, do the following:
1. Enter the Global Lock of NVPBs mode.
2. Set the Global Lock Bit to ‘0’, and verify the
value.
3. Exit the Global Lock of NVPBs mode.
4. Enter the Password Commands mode.
5. Submit the 64-bit password with the Submit
Password command.
6. Wait 2 µs for the device to verify the password.
7. Exit the Password Commands mode.
8. Re-enter the Global Lock of NVPBs mode
9. Read the Global Lock Bit with the Global Lock
Bit Status Read command. The Global Lock bit
should now be ‘1’.
After verifying the password, program the DQ₂ and
DQ₁ OTP bits of the PSR to explicitly choose Password
mode. Once the Password mode has been selected,
the Password Read and Password Program com-
mands are permanently disabled. There is no longer
any method for reading or modifying the password. In
addition, Microchip is unable to read or modify the
password. If a Password Read command is issued
while in Password mode, the data presented for each
word of the password is FFFFh.
If the Password Mode is not explicitly chosen in the
PSR, then the password can still be read and modified.
Therefore, Microchip strongly recommends that users
explicitly choose Password Mode in the PSR.
4.17 Irreversible Block Locking
The SST38VF6401B/6402B/6403B/6404B provides
Irreversible Block Locking, a feature that allows users
to customize the size of Read-Only Memory (ROM) on
the device and provides more flexibility than One-Time
Programmable (OTP) memory.
Applying Irreversible Block Locking turns user-selected
memory areas into ROM by permanently disabling Pro-
gram and Erase operations to these chosen areas. Any
area that becomes ROM cannot be changed back to
Flash.
Any memory blocks in the main memory, including boot
blocks, can be irreversibly locked. In non-uniform boot
block devices (SST38VF6403B and SST38VF6404B)
each 4 KW block in the boot area can be irreversibly
locked. If desired, all blocks in the main memory can be
irreversibly locked.
To use Irreversible Block Locking do the following:
1. Global Lock Bit should be ‘1’. The Irreversible
Block Lock command is disabled when Global
Lock Bit is ‘0’.
2. Enter the Non-Volatile Block Protection mode.
3. Use the NVPB Program command to protect
only the blocks that are to be changed into
ROM.
4. Exit the Non-Volatile Block Protection mode.
5. Issue the Irreversible Block Lock command (see
Table 5-2 for details).
The Irreversible Block Lock command can only be used
once. Issuing the command after the first time has no
effect on the device.
Important: Once the Irreversible Block Lock command
is used, the state of the NVPBs can no longer be
changed or overridden. Therefore, the following fea-
tures no longer have any effect on the device:
• Global Lock of NVPBs feature
• Password feature
• NVPB Program command
• NVPB Erase command
• DQ2 and DQ1 of PSR
In addition, WP# has no effect on any memory in the
boot block area that has been irreversibly locked.
 2013 Microchip Technology Inc.
Preliminary
DS25002B-page 15