M29DW128F datasheet(24/94 Pages) STMICROELECTRONICS

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Software Protection

M29DW128F

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5.1.2

Non-Volatile Protection

A Non-Volatile Modify Protection bit is assigned to each block or group of blocks.

When a Non-Volatile Modify Protection bit is set to ‘1’ the associated block or group of

blocks is protected, preventing any program or erase operations in this block or group of

blocks.

The Non-Volatile Modify Protection bits are set individually by issuing a Set Non-Volatile

Modify Protection bit command. They are non-volatile and will remain set through a

hardware reset or a power-down/power-up sequence.

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 Section 6.3.5: Password Program command and Section 6.3.6: 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).

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