M28R400CT datasheet(12/48 Pages) STMICROELECTRONICS

12 / 48 page

M28R400CT, M28R400CB

12/48

ure 19., Erase Suspend & Resume Flowchart and

Pseudo Code, for flowcharts for using the Pro-

gram/Erase Resume command.

Protection Register Program Command

The Protection Register Program command is

used to Program the 64 bit user One-Time-Pro-

grammable (OTP) segment of the Protection Reg-

ister. The segment is programmed 16 bits at a

time. When shipped all bits in the segment are set

to ‘1’. The user can only program the bits to ‘0’.

Two write cycles are required to issue the Protec-

tion Register Program command.

■

The first bus cycle sets up the Protection

■

The second latches the Address and the Data

to be written to the Protection Register and

starts the Program/Erase Controller.

Read operations output the Status Register con-

tent after the programming has started.

The segment can be protected by programming bit

1 of the Protection Lock Register. Bit 1 of the Pro-

tection Lock Register protects bit 2 of the Protec-

tion Lock Register. Programming bit 2 of the

Protection Lock Register will result in a permanent

protection of the Security Block (see Figure 5., Se-

curity Block Memory Map). Attempting to program

a previously protected Protection Register will re-

sult in a Status Register error. The protection of

the Protection Register and/or the Security Block

is not reversible.

The Protection Register Program cannot be sus-

pended. See APPENDIX C., Figure 21., Protec-

tion Register Program Flowchart and Pseudo

Code, for the flowchart for using the Protection

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 9. shows the protection status after issuing

a Block Lock command.

The Block Lock bits are volatile, once set they re-

main set until a hardware reset or power-down/

power-up. They are cleared by a Blocks Unlock

command. Refer to the section, BLOCK LOCK-

ING, for a detailed explanation.

Block Unlock Command

The Blocks Unlock command is used to unlock a

block, allowing the block to be programmed or

erased. Two Bus Write cycles are required to is-

sue the Blocks 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 9. shows the protection status after issuing

a Block Unlock command. Refer to the section,

BLOCK LOCKING, for a detailed explanation.

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 com-

mand.

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 9. 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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