M95640-A145 datasheet(13/44 Pages) STMICROELECTRONICS

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M95640-A125 M95640-A145

Operating features

SRWD bit and W input signal

The Status Register Write Disable (SRWD) bit is operated in conjunction with the Write

Protect pin (W) signal. When the SRWD bit is written to 0, it is possible to write the Status

When the SRWD bit is written to 1, two cases have to be considered, depending on the

state of the W input pin:

•

Case 1: if pin W is driven high, it is possible to write the Status Register.

•

Case 2: if pin W is driven low, it is not possible to write the Status Register (WRSR is

discarded) and therefore SRWD,BP1,BP0 bits cannot be changed (the size of the

protected memory block defined by BP1,BP0 bits is frozen).

Case 2 can be entered in either sequence:

•

Writing SRWD bit to 1 after driving pin W low, or

•

Driving pin W low after writing SRWD bit to 1.

The only way to exit Case 2 is to pull pin W high.

Note: if pin W is permanently tied high, the Status Register cannot be write-protected.

The protection features of the device are summarized in Table 4.

3.5

Identification page

The M95640-A125 and M95640-A145 offer an Identification page (32 byte) in addition to the

64 Kbit memory. The Identification page contains two fields:

•

Device identification: the three first byte are programmed by STMicroelectronics with

the Device identification code, as shown in Table 5.

•

Application parameters: the bytes after the Device identification code are available for

application specific data.

Table 3. Write-protected block size

Status Register bits

Protected block

Protected array addresses

BP1

BP0

None

Upper quarter

1800h - 1FFFh

Upper half

1000h - 1FFFh

Whole memory

0000h - 1FFFh plus Identification page

Table 4. Protection modes

SRWD bit

W signal

Status

Status Register is writable.

Status Register is write-protected.

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