M25P40 datasheet(16/40 Pages) STMICROELECTRONICS

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M25P40

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Write Status Register (WRSR)

The Write Status Register (WRSR) instruction al-

lows new values to be written to the Status Regis-

ter. Before it can be accepted, a Write Enable

(WREN) instruction must previously have been ex-

ecuted. After the Write Enable (WREN) instruction

has been decoded and executed, the device sets

the Write Enable Latch (WEL).

The Write Status Register (WRSR) instruction is

entered by driving Chip Select (S) Low, followed

by the instruction code and the data byte on Serial

Data Input (D).

The instruction sequence is shown in Figure 11..

The Write Status Register (WRSR) instruction has

no effect on b6, b5, b1 and b0 of the Status Reg-

ister. b6 and b5 are always read as 0.

Chip Select (S) must be driven High after the

eighth bit of the data byte has been latched in. If

not, the Write Status Register (WRSR) instruction

is not executed. As soon as Chip Select (S) is driv-

en High, the self-timed Write Status Register cycle

(whose duration is tW) is initiated. While the Write

Status Register cycle is in progress, the Status

Write In Progress (WIP) bit. The Write In Progress

(WIP) bit is 1 during the self-timed Write Status

When the cycle is completed, the Write Enable

Latch (WEL) is reset.

The Write Status Register (WRSR) instruction al-

lows the user to change the values of the Block

Protect (BP2, BP1, BP0) bits, to define the size of

the area that is to be treated as read-only, as de-

fined in Table 2.. The Write Status Register

(WRSR) instruction also allows the user to set or

reset the Status Register Write Disable (SRWD)

bit in accordance with the Write Protect (W) signal.

The Status Register Write Disable (SRWD) bit and

Write Protect (W) signal allow the device to be put

in the Hardware Protected Mode (HPM). The Write

Status Register (WRSR) instruction is not execut-

ed once the Hardware Protected Mode (HPM) is

entered.

Figure 11. Write Status Register (WRSR) Instruction Sequence

AI02282D

3456789 10 11 12 13 14 15

High Impedance

Instruction

Status

765432

MSB

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