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M95128-DW3/P

128 Kbit Serial SPI bus EEPROM with high speed clock

STMicroelectronics 

M95128, M95128-W, M95128-R

Instructions

5.4

Write Status Register (WRSR)

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

Register. Before it can be accepted, a Write Enable (WREN) instruction must previously

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 8.

The Write Status Register (WRSR) instruction has no effect on b6, b5, b4, b1 and b0 of the

Status Register. b6, b5 and b4 are always read as 0.

Chip Select (S) must be driven High after the rising edge of Serial Clock (C) that latches in

the eighth bit of the data byte, and before the next rising edge of Serial Clock (C). Otherwise,

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 (BP1, BP0) bits, to define the size of the area that is to be treated as read-

only, as defined in Table 4.

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 contents of the Status Register Write Disable (SRWD) and Block Protect (BP1, BP0)

bits are frozen at their current values from just before the start of the execution of Write

Status Register (WRSR) instruction. The new, updated, values take effect at the moment of

completion of the execution of Write Status Register (WRSR) instruction.

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