M28W320FCT datasheet(21/69 Pages) STMICROELECTRONICS

21 / 69 page

M28W320FCT, M28W320FCB

Command interface

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4.13

Block Lock command

The Block Lock command is used to lock a block and prevent Program or Erase operations

from changing the data in it. All blocks are locked at power-up or reset.

Two Bus Write cycles are required to issue the Block Lock command.

The first bus cycle sets up the Block Lock command.

The second Bus Write cycle latches the block address.

The lock status can be monitored for each block using the Read Electronic Signature

command. Table 10 shows the protection status after issuing a Block Lock command.

The Block Lock bits are volatile, once set they remain set until a hardware reset or power-

down/power-up. They are cleared by a Blocks Unlock command. Refer to the section, Block

Locking, for a detailed explanation.

4.14

Block Unlock command

The Block Unlock command is used to unlock a block, allowing the block to be programmed

or erased. Two Bus Write cycles are required to issue the Block Unlock command.

The first bus cycle sets up the Block Unlock command.

The second Bus Write cycle latches the block address.

The lock status can be monitored for each block using the Read Electronic Signature

command. Table 10 shows the protection status after issuing a Block Unlock command.

Refer to the section, Block Locking, for a detailed explanation.

4.15

Block Lock-Down command

A locked block cannot be Programmed or Erased, or have its protection status changed

when WP is low, VIL. When WP is high, VIH, the Lock-Down function is disabled and the

locked blocks can be individually unlocked by the Block Unlock command.

Two Bus Write cycles are required to issue the Block Lock-Down command.

The first bus cycle sets up the Block Lock command.

The second Bus Write cycle latches the block address.

The lock status can be monitored for each block using the Read Electronic Signature

command. Locked-Down blocks revert to the locked (and not locked-down) state when the

device is reset on power-down. Table 10 shows the protection status after issuing a Block

Lock-Down command. Refer to the section, Block Locking, for a detailed explanation.

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