M28W320FCT datasheet(25/69 Pages) STMICROELECTRONICS

25 / 69 page

M28W320FCT, M28W320FCB

Block locking

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Block locking

The M28W320FCT and M28W320FCB feature an instant, individual block locking scheme

that allows any block to be locked or unlocked with no latency. This locking scheme has

three levels of protection.

●

Lock/Unlock - this first level allows software-only control of block locking.

●

Lock-Down - this second level requires hardware interaction before locking can be

changed.

●

VPP ≤ VPPLK - the third level offers a complete hardware protection against program

and erase on all blocks.

The protection status of each block can be set to Locked, Unlocked, and Lock-Down.

Table 10 defines all of the possible protection states (WP, DQ1, DQ0), and Appendix C,

Figure 22, shows a flowchart for the locking operations.

5.1

Reading a Block’s Lock Status

The lock status of every block can be read in the Read Electronic Signature mode of the

device. To enter this mode write 90h to the device. Subsequent reads at the address

specified in Table 6, will output the protection status of that block. The lock status is

represented by DQ0 and DQ1. DQ0 indicates the Block Lock/Unlock status and is set by the

Lock command and cleared by the Unlock command. It is also automatically set when

entering Lock-Down. DQ1 indicates the Lock-Down status and is set by the Lock-Down

command. It cannot be cleared by software, only by a hardware reset or power-down.

The following sections explain the operation of the locking system.

5.2

Locked state

The default status of all blocks on power-up or after a hardware reset is Locked (states

(0,0,1) or (1,0,1)). Locked blocks are fully protected from any program or erase. Any

program or erase operations attempted on a locked block will return an error in the Status

appropriate software commands. An Unlocked block can be Locked by issuing the Lock

command.

5.3

Unlocked state

Unlocked blocks (states (0,0,0), (1,0,0) (1,1,0)), can be programmed or erased. All unlocked

blocks return to the Locked state after a hardware reset or when the device is powered-

down. The status of an unlocked block can be changed to Locked or Locked-Down using the

appropriate software commands. A locked block can be unlocked by issuing the Unlock

command.

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