M950X0-W datasheet(14/46 Pages) STMICROELECTRONICS

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Operating features

M950x0-W M950x0-R M950x0-DF

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DocID6512 Rev 13

4.3

Data protection and protocol control

To help protect the device from data corruption in noisy or poorly controlled environments, a

number of safety features have been built in to the device. The main security measures can

be summarized as follows:

•

WEL bit is reset at power-up.

•

Chip Select (S) must rise after the eighth clock count (or multiple thereof) in order to

start a non-volatile Write cycle (in the memory array or in the Status register).

•

Accesses to the memory array are ignored during the non-volatile programming cycle,

and the programming cycle continues unaffected.

•

Invalid Chip Select (S) and Hold (HOLD) transitions are ignored.

For any instruction to be accepted and executed, Chip Select (S) must be driven high after

the rising edge of Serial Clock (C) that latches the last bit of the instruction, and before the

next rising edge of Serial Clock (C).

For this, “the last bit of the instruction” can be the eighth bit of the instruction code, or the

eighth bit of a data byte, depending on the instruction (except in the case of RDSR and

READ instructions). Moreover, the “next rising edge of CLOCK” might (or might not) be the

next bus transaction for some other device on the bus.

When a Write cycle is in progress, the device protects it against external interruption by

ignoring any subsequent READ, WRITE or WRSR instruction until the present cycle is

complete.

Table 3. Write-protected block size

Status register bits

Protected block

Protected array addresses

BP1

BP0

M95040

M95020

M95010

none

Upper quarter

180h - 1FFh

C0h - FFh

60h - 7Fh

Upper half

100h - 1FFh

80h - FFh

40h - 7Fh

Whole memory

000h - 1FFh

00h - FFh

00h - 7Fh

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