Datasheet

64 Mbit (x16) Advanced Multi-Purpose Flash Plus

SST38VF6401 / SST38VF6402 / SST38VF6403 / SST38VF6404

Data Sheet

Microchip Technology Company

Irreversible Block Locking

The SST38VF6401/6402/6403/6404 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 dis-

abling Program 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-uni-

form boot block devices (SST38VF6403 and SST38VF6404) each 4 KW sector 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 11 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 features 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.

To verify whether the Irreversible Block Lock command has already been issued, enter the Product ID

mode and read address 5FEH. If DQ

= 0, then Irreversible Block Lock has already been executed.

When using this feature to determine if a specific block is ROM, use the NVPB Status Read.