M25P128 datasheet(21/41 Pages) STMICROELECTRONICS

21 / 41 page

M25P128

Instructions

Rev. 1

21/41

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 12.

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.

The protection features of the device are summarized in Table 7

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 Write Enable

Table 7.

Protection Modes

Signal

SRWD

Bit

Mode

Write Protection of the

Status Register

Memory Content

Protected Area(1)

As defined by the values in the Block Protect (BP2, BP1, BP0) bits of the Status Register, as shown in

Table 2: Protected Area Sizes.

Unprotected Area(1)

Software

Protected

(SPM)

Status Register is Writable

(if the WREN instruction

has set the WEL bit)

The values in the SRWD,

BP2, BP1 and BP0 bits

can be changed

Protected against

Page Program,

Sector Erase and

Bulk Erase

Ready to accept

Page Program and

Sector Erase

instructions

Hardware

Protected

(HPM)

Status Register is

Hardware write protected

The values in the SRWD,

BP2, BP1 and BP0 bits

cannot be changed

Protected against

Page Program,

Sector Erase and

Bulk Erase

Ready to accept

Page Program and

Sector Erase

instructions

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