M28W320CT datasheet(14/42 Pages) STMICROELECTRONICS

14 / 42 page

M28W320CT, M28W320CB

14/42

BLOCK PROTECTION

The M28W320C provide a flexible protection of all

the memory providing the protection unprotection

and locking of any blocks. All blocks are protected

at power-up. Each block of the array has two lev-

els of protection against program or erase opera-

tion. The first level is set by the Block Protect

instruction; a protected block cannot be pro-

grammed or erased until a Block Unprotect in-

struction is given for that block. A second level of

protection is set by the Block Lock instruction, and

requires the use of the WP pin, according to the

following scheme:

– when WP is at VIH, the Lock status is overridden

and all blocks can be protected or unprotected;

– when WP is at VIL, Lock status is enabled; the

locked blocks are protected, regardless of their

previous protect state, and protection status

cannot be changed. Blocks that are not locked

can still change their protection status;

– the lock status is cleared for all blocks at power

up.

The protection and lock status can be monitored

for each block using the Read Electronic Signature

(RSIG) instruction. Protected blocks will output a

’1’ on DQ0 and locked blocks will output a ’1’ in

DQ1.

PROTECTION REGISTER

and SECURITY BLOCK

The M28W320C features a 128-bit protection reg-

ister and a security Block in order to increase the

protection of a system design. The Protection

segment (81h to 84h) is a unique device number,

while the second one (85h to 88h) can be pro-

grammed by the user. When shipped the user pro-

grammable segment is read at ’1’. It can be only

programmed at ’0’;

The user programmable segment can be protect-

ed writing the bit 1 of the Protection Lock register

(80h). The bit 1 protect also the bit 2 of the Protec-

tion Lock Register. The M28W320C feature a se-

curity Block. The security Block is located at

1FF000-1FFFFF (M28W320CT) or at 000000-

000FFF (M28W320CB) of the device. This block

can be permanently protected by the user pro-

gramming the bit 2 of the Protection Lock Register.

The protection Register and the Protection Lock

subsequent read in the address starting from 80h

to 88h, the user will retrieve respectively the Pro-

tection Lock register, the unique device number

segment and the OTP user programmable register

segment (see Table 8).

Figure 4. Security Block Memory Map

AI03523

Parameter Block # 0

User Programmable OTP

Unique device number

Protection Register Lock

88h

85h

84h

81h

80h

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