M58PR256J datasheet(62/114 Pages) STMICROELECTRONICS

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Block locking

M58PR256J, M58PR512J

62/114

Block locking

The M58PRxxxJ features 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 Locked-Down.

Table 21, defines all of the possible protection states (WP, DQ1, DQ0), and Appendix C,

Figure 25, shows a flowchart for the locking operations.

12.1

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 issue the Read Electronic Signature command. Subsequent

reads at the address specified in Table 9, 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. DQ0 is

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

by the Lock-Down command. DQ1 cannot be cleared by software, only by a hardware reset

or power-down.

The following sections explain the operation of the locking system.

12.2

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 program or erase operations. Any

program or erase operations attempted on a Locked Block will return an error in the Status

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

command.

12.3

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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