ST92F120 datasheet(51/324 Pages) STMICROELECTRONICS

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ST92F120 - SINGLE VOLTAGE FLASH & EEPROM

PROTECTION STRATEGY (Cont’d)

Bits 2:0 = PWT[2:0]:

Password Attempt 2-0.

If the TMDIS bit in the NVWPR register (231FFDh)

is programmed to 0, every time a Set Protection

operation is executed with Program Addresses

equal to NVPWD1-0 (231FFE-Fh), the two provid-

Program

Data

are

compared

with

the

NVPWD1-0 content; if there is not a match one of

PWT2-0 bits is automatically programmed to 0:

when these three bits are all programmed to 0 the

test modes are disabled forever. In order to inten-

tionally disable test modes forever, it is sufficient to

set a random Password and then to make 3 wrong

attempts to enter it.

NON VOLATILE WRITE PROTECTION REGIS-

TER (NVWPR)

Address: 231FFDh - Read/Write

Delivery value: 1111 1111 (FFh)

Bit 7 = TMDIS:

Test mode disable (Read Only).

This bit, if set to 1, allows to bypass all the protec-

tions in test and EPB modes. If programmed to 0,

on the contrary, all the protections remain active

also in test mode. The only way to enable the test

modes if this bit is programmed to 0, is to execute

the Set Protection operation with Program Ad-

dresses equal to NVPWD1-0 (231FFF-Eh) and

Program Data matching with the content of

NVPWD1-0. This bit is read only: it is automatically

programmed to 0 when NVPWD1-0 are written for

the first time.

0: Test mode disabled

1: Test mode enabled

Bit 6 = PWOK:

Password OK (Read Only).

If the TMDIS bit is programmed to 0, when the Set

Protection operation is executed with Program Ad-

dresses equal to NVPWD[1:0] and Program Data

matching with NVPWD[1:0] content, the PWOK bit

is automatically programmed to 0. When this bit is

programmed to 0 TMDIS protection is bypassed

and the test and EPB modes are enabled.

0: Password OK

1: Password not OK

Bit 5 = WPBR:

TestFlash Write Protection.

This bit, if programmed at 0, disables any write ac-

cess to the TestFlash address space. This protec-

tion cannot be temporarily disabled.

0: TestFlash write protection on

1: TestFlash write protection off

Note: it is strongly advised to never program the

WPBR bit in the NVWPR register, as this will pre-

vent any further write access to the protection reg-

isters.

Bit 4 = WPEE:

EEPROM Write Protection.

This bit, if programmed to 0, disables any write ac-

cess to the EEPROM address space. This protec-

tion can be temporary disabled by executing the

Set Protection operation and writing 1 into this bit.

To restore the protection it needs to reset the mi-

cro or to execute another Set Protection operation

and write 0 to this bit.

0: EEPROM write protection on

1: EEPROM write protection off

Bits 3:0 = WPRS[3:0]:

ROM Segments 3-0 Write

Protection.

These bits, if programmed to 0, disable any write

access to the 4 Flash sectors address spaces.

These protections can be temporary disabled by

executing the Set Protection operation and writing

1 into these bits. To restore the protection it needs

to reset the micro or to execute another Set Pro-

tection operation and write 0 into these bits.

0: ROM Segments 3-0 write protection on

1: ROM Segments 3-0 write protection off

NON VOLATILE PASSWORD (NVPWD1-0)

Address: 231FFF-231FFEh - Write Only

Delivery value: 1111 1111 (FFh)

Bits 7:0 = PWD[7:0]:

Password bits 7:0 (Write On-

ly).

These bits must be programmed with the Non Vol-

atile Password that must be provided with the Set

Protection operation to disable (first write access)

or to reenable (second write access) the test and

EPB modes. The first write access fixes the pass-

word value and resets the TMDIS bit of NVWPR

TMDI

PWO

WPB

WPE

WPRS

654

321

PWD

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