28F004SC datasheet(20/42 Pages) INTEL

20 / 42 page

BYTE-WIDE SmartVoltage FlashFile™ MEMORY FAMILY

PRELIMINARY

4.10

Clear Block Lock-Bits

Command

All set block lock-bits are cleared in parallel via the

Clear Block Lock-Bits command. With the master

lock-bit not set, block lock-bits can be cleared using

only the Clear Block Lock-Bits command. If the

master lock-bit is set, clearing block lock-bits

requires both the Clear Block Lock-Bits command

and VHH on the RP# pin. See Table 6 for a

summary of hardware and software write protection

options.

Clear block lock-bits operation is initiated using a

two-cycle command sequence.

clear

block

lock-bits setup is written first. Then, the device

automatically outputs status register data when

read (see Figure 12). The CPU can detect

completion of the clear block lock-bits event by

analyzing the RY/BY# pin output or status register

bit SR.7.

When the operation is complete, status register bit

SR.5 should be checked. If a clear block lock-bit

error is detected, the status register should be

cleared. The CUI will remain in read status register

mode until another command is issued.

This two-step sequence of set-up followed by

execution ensures that block lock-bits are not

accidentally

cleared.

invalid

Clear

Block

Lock-Bits command sequence will result in status

reliable clear block lock-bits operation can only

occur when VCC = VCC2/3 and VPP = VPPH1/2/3. If a

clear block lock-bits operation is attempted while

VPP

≤ VPPLK, SR.3 and SR.5 will be set to “1.” In the

absence of this high voltage, the block lock-bits

content are protected against alteration. A suc-

cessful clear block lock-bits operation requires that

the master lock-bit is not set or, if the master lock-

bit is set, that RP# = VHH. If it is attempted with the

master lock-bit set and RP# = VIH, SR.1 and SR.5

will be set to “1” and the operation will fail. A clear

block lock-bits operation with VIH < RP# < VHH

produce spurious

results

and

should

not

attempted.

If a clear block lock-bits operation is aborted due to

VPP or VCC transitioning out of valid range or RP#

active transition, block lock-bit values are left in an

undetermined state. A repeat of clear block lock-

bits is required to initialize block lock-bit contents to

known values. Once the master lock-bit is set, it

cannot be cleared.

Table 6. Write Protection Alternatives

Operation

Master

Lock-Bit

Block

Lock-Bit

RP#

Effect

Block Erase or

VIH or VHH

Block Erase and Program Enabled

Program

VIH

Block is Locked. Block Erase and Program Disabled

VHH

Block Lock-Bit Override. Block Erase and Program

Enabled

Set Block

VIH or VHH

Set Block Lock-Bit Enabled

Lock-Bit

VIH

Master Lock-Bit is Set. Set Block Lock-Bit Disabled

VHH

Master Lock-Bit Override. Set Block Lock-Bit

Enabled

Set Master

VIH

Set Master Lock-Bit Disabled

Lock-Bit

VHH

Set Master Lock-Bit Enabled

Clear Block

VIH or VHH

Clear Block Lock-Bits Enabled

Lock-Bits

VIH

Master Lock-Bit is Set. Clear Block Lock-Bits

Disabled

VHH

Master Lock-Bit Override. Clear Block Lock-Bits

Enabled

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