M95256 datasheet(19/48 Pages) STMICROELECTRONICS

19 / 48 page

M95256-DR, M95256, M95256-W, M95256-R

Instructions

Doc ID 12276 Rev 11

19/48

The protection features of the device are summarized in Table 6.

When the Status Register Write Disable (SRWD) bit of the Status Register is 0 (its initial

delivery state), it is possible to write to the Status Register (provided that the WEL bit has

previously been set by a WREN instruction), regardless of the logic level applied on the

Write Protect (W) input pin.

When the Status Register Write Disable (SRWD) bit of the Status Register is set to 1, two

cases need to be considered, depending on the state of Write Protect (W) input pin:

●

If Write Protect (W) input pin is driven high, it is possible to write to the Status Register

(provided that the WEL bit has previously been set by a WREN instruction.

●

If Write Protect (W) input pin is driven low, it is not possible to write to the Status

to write to the Status Register are rejected, and are not accepted for execution). As a

consequence, all the data bytes in the memory area that are software protected (SPM)

by the Block Protect (BP1, BP0) bits of the Status Register, are also hardware

protected against data modification.

Regardless of the order of the two events, the Hardware Protected Mode (HPM) can be

entered:

●

either by setting the SRWD bit after driving Write Protect (W) input pin low,

●

or by driving Write Protect (W) input pin low after setting the SRWD bit.

Once entered in the Hardware Protected mode (HPM), the only way to exit the HPM mode is

to pull high the Write Protect (W) input pin.

If Write Protect (W) input pin is permanently tied high, the Hardware Protected mode (HPM)

can never be activated, and only the Software Protected mode (SPM), using the Block

Protect (BP1, BP0) bits of the Status Register, can be used.

Figure 9.

Write Status Register (WRSR) sequence

AI02282D

3456789 10 11 12 13 14 15

High Impedance

Instruction

Status

765432

MSB

M95256 数据表(PDF) 19 Page - STMicroelectronics

M95256 数据表(HTML) 19 Page - STMicroelectronics

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48

数据表下载