M25P40 datasheet(24/53 Pages) STMICROELECTRONICS

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Instructions

M25P40

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6.5

Write Status Register (WRSR)

The Write Status Register (WRSR) instruction allows new values to be written to the Status

have been executed. 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 Register. 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 driven 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 Register may still

be read to check the value of the Write In Progress (WIP) bit. The Write In Progress (WIP)

bit is 1 during the self-timed Write Status Register cycle, and is 0 when it is completed.

When the cycle is completed, the Write Enable Latch (WEL) is reset.

The Write Status Register (WRSR) instruction allows 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 defined 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 executed 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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