M29DW128F datasheet(24/93 Pages) STMICROELECTRONICS

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5 Software Protection

M29DW128F

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The Non-Volatile Modify Protection bits cannot be cleared individually, they can only be cleared

all at the same time by issuing a Clear Non-Volatile Modify Protection Bits command.

However if any one of the Non-Volatile Modify Protection bits has to be cleared, care should be

taken to preprogram to ‘1’ all the Non-Volatile Modify Protection Bits prior to issuing the Clear

Non-Volatile Modify Protection bits in order to prevent the over-erasure of previously cleared

Non Volatile Modify Protection bits. It is crucial to prevent over-erasure because the process

may lead to permanent damage to the Non-Volatile Modify Protection Bits and the device does

not have any built-in means of preventing over-erasure.

The device features a volatile Lock-Down bit which can be used to prevent changing the state

of the Non-Volatile Modify Protection bits. When set to ‘1’, the Non-Volatile Modify Protection

bits can no longer be modified; when set to ‘0’, the Non-Volatile Modify Protection bits can be

set and reset using the Set Non-Volatile Modify Protection Bit command and the Clear Non-

Volatile Modify Protection Bits command, respectively.

The Lock-Down bit is set by issuing the Set Lock-Down Bit Command. It is not cleared using a

command, but through a hardware reset or a power-down/power-up sequence.

The parts are shipped with the Non-Volatile Modify Protection bits set to ‘0’.

Locked blocks and Non-Volatile Locked blocks can co-exist in the same memory array.

Refer to Table 10: Block Protection Status and Figure 7: Software Protection Scheme for details

on the block protection mechanism.

5.2

Password Protection Mode

The Password Protection mode provides a more advanced level of software protection than the

Standard Protection mode.

Prior to entering the Password Protection mode, it is necessary to set a password and to verify

it (see Password Program command and Password Verify command). The Password Protection

mode is then activated by programming the Password Protection Mode Lock bit to ‘1’. The

Reset/Block Temporary Unprotect pin, RP, can be at VID or at VIH.

This operation is not reversible and once the bit is programmed the device will permanently

remain in the Password Protection mode.

The Password Protection mode uses the same protection mechanisms as the Standard

Protection mode (Block Lock/Unlock, Non-Volatile Protection).

5.2.1

Block Lock/Unlock Protection

The Block Lock/Unlock Protection operates exactly in the same way as in the Standard

Protection mode.

5.2.2

Non-Volatile Protection

The Non-Volatile Protection is more advanced in the Password Protection mode.

In this mode, the Lock-Down bit cannot be cleared through a hardware reset or a power-down/

power-up sequence.

The Lock-Down bit is cleared by issuing the Password Protection Unlock command along with

the correct password.

M29DW128F Datasheet(PDF) 24 Page - STMicroelectronics

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