M29DW128F datasheet(39/93 Pages) STMICROELECTRONICS

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M29DW128F

6 Command Interface

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The fourth cycle inputs the 16-bit data required to program the Password.

To program the 64-bit Password, the complete command sequence must be entered four times

at four consecutive addresses selected by A1 to A0.

Read operations can be used to read the Status Register during a Password Program

operation. All other operations are forbidden.

The Password can be checked by issuing a Password Verify command.

Once Password Program operation has completed, a Read/ Reset command must be issued to

return the device to Read mode. The Password Protection mode can then be selected.

By default, all Password bits are set to ‘1’.

6.3.6

Password Verify command

The Password Verify Command is used to verify the Password used in Password Protection

mode. To verify the 64-bit Password, the complete command sequence must be entered four

times at four consecutive addresses selected by A1 to A0. If the Password Mode Locking Bit is

programmed and the user attempts to verify the Password, the device will output all F’s onto the

I/O data bus. The Password is output regardless of the bank address.

The user must issue a Read/reset command to return the device to Read mode.

Dual operations are not allowed during a Password Verify operation.

6.3.7

Password Protection Unlock command

The Password Protection Unlock command is used to clear the Lock-Down bit in order to

unprotect all Non-Volatile Modify Protection bits when the device is in Password Protection

mode. The Password Protection Unlock command must be issued along with the correct

Password.

The complete command sequence must be entered for each 16 bits of the Password.

There must be a 2µs delay between successive Password Protection Unlock commands in

order to prevent hackers from cracking the Password by trying all possible 64-bit combinations.

If this delay is not respected, the latest command will be ignored.

6.3.8

Set Password Protection Mode command

The Set Password Protection Mode command puts the device in Password Protection mode by

programming the Password Protection Mode Lock bit to ‘1’. This command can be issued either

with the Reset/Block Temporary Unprotect pin, RP, at VID or at VIH.

Six cycles are required to issue a Set Password Protection Mode command:

The first two cycles are unlock cycles.

The third cycle issues the command.

The fourth and fifth cycles select the address (see Table 17: Protection Command

Addresses).

The last cycle verifies if the operation has been successful. If DQ0 is set to ’1’, the device

has successfully entered the Password Protection mode. If DQ0 is ‘0’, the operation has

failed and the command must be re-issued.

There must be a 100µs delay between the fourth and fifth cycles.

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