M95128-WDL3T Ver la hoja de datos (PDF) - STMicroelectronics

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M95128-WDL3T

256/128 Kbit Serial SPI Bus EEPROM With High Speed Clock

STMicroelectronics 

Table 6. Write Protected Block Size

Status Register Bits

BP1

BP0

Protected Block

0

0

none

0

1

Upper quarter

1

0

Upper half

1

1

Whole memory

M95256, M95128

Array Addresses Protected

M95256

M95128

none

none

6000h - 7FFFh

3000h - 3FFFh

4000h - 7FFFh

2000h - 3FFFh

0000h - 7FFFh

0000h - 3FFFh

The size of the write-protection area applies equal-

ly in SPM and HPM. The BP1 and BP0 bits of the

status register have the appropriate value (see Ta-

ble 6) written into them after the contents of the

protected area of the EEPROM have been written.

The initial delivery state of the BP1 and BP0 bits is

00, indicating a write-protection size of 0.

Software Protected Mode (SPM)

The act of writing a non-zero value to the BP1 and

BP0 bits causes the Software Protected Mode

(SPM) to be started. All attempts to write a byte or

page in the protected area are ignored, even if the

Write Enable Latch is set. However, writing is still

allowed in the unprotected area of the memory ar-

ray and to the SRWD, BP1 and BP0 bits of the sta-

tus register, provided that the WEL bit is first set.

Hardware Protected Mode (HPM)

The Hardware Protected Mode (HPM) offers a

higher level of protection, and can be selected by

setting the SRWD bit after pulling down the W pin

or by pulling down the W pin after setting the

SRWD bit. The SRWD is set by the WSR instruc-

tion, provided that the WEL bit is first set. The set-

ting of the SRWD bit can be made independently

of, or at the same time as, writing a new value to

the BP1 and BP0 bits.

Once the device is in the Hardware Protected

Mode, the data bytes in the protected area of the

memory array, and the content of the status regis-

ter, are write-protected. The only way to re-enable

writing new values to the status register is to pull

the W pin high. This cause the device to leave the

Hardware Protected Mode, and to revert to being

in the Software Protected Mode. (The value in the

BP1 and BP0 bits will not have been changed).

Further details of the operation of the Write Protect

pin (W) is given earlier, on page 3.

Typical Use of HPM and SPM

The W pin can be dynamically driven by an output

port of a microcontroller. It is also possible,

though, to connect it permanently to VSS (by a sol-

der connection, or through a pull-down resistor).

The manufacturer of such a printed circuit board

can take the memory device, still in its initial deliv-

ery state, and can solder it directly on to the board.

After power on, the microcontroller can be instruct-

ed to write the protected data into the appropriate

area of the memory. When it has finished, the ap-

propriate values are written to the BP1, BP0 and

Figure 8. WRSR: Write Status Register Sequence

S

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

C

INSTRUCTION

STATUS REG.

D

76543210

MSB

HIGH IMPEDANCE

Q

AI02282

7/20

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