MX25L12845E
(5) Write Status Register (WRSR)
The WRSR instruction is for changing the values of Status Register Bits. Before sending WRSR instruction, the
Write Enable (WREN) instruction must be decoded and executed to set the Write Enable Latch (WEL) bit in ad-
vance. The WRSR instruction can change the value of Block Protect (BP3, BP2, BP1, BP0) bits to define the pro-
tected area of memory (as shown in Table 2). The WRSR also can set or reset the Quad enable (QE) bit and set or
reset the Status Register Write Disable (SRWD) bit in accordance with Write Protection (WP#/SIO2) pin signal, but
has no effect on bit1(WEL) and bit0 (WIP) of the statur register. The WRSR instruction cannot be executed once the
Hardware Protected Mode (HPM) is entered.
The sequence of issuing WRSR instruction is: CS# goes low→ sending WRSR instruction code→ Status Register
data on SI→ CS# goes high. (see Figure 16)
The CS# must go high exactly at the byte boundary; otherwise, the instruction will be rejected and not executed.
The self-timed Write Status Register cycle time (tW) is initiated as soon as Chip Select (CS#) goes high. The Write
in Progress (WIP) bit still can be check out during the Write Status Register cycle is in progress. The WIP sets 1
during the tW timing, and sets 0 when Write Status Register Cycle is completed, and the Write Enable Latch (WEL)
bit is reset.
Protection Modes
Mode
Status register condition
WP# and SRWD bit status
Memory
Status register can be written
in (WEL bit is set to "1") and
the SRWD, BP0-BP3
Software protection
mode(SPM)
WP#=1 and SRWD bit=0, or
WP#=0 and SRWD bit=0, or
WP#=1 and SRWD=1
The protected area
cannot
be program or erase.
bits can be changed
The SRWD, BP0-BP3 of
status register bits cannot be
changed
The protected area
cannot
be program or erase.
Hardware protection
mode (HPM)
WP#=0, SRWD bit=1
Note: As defined by the values in the Block Protect (BP3, BP2, BP1, BP0) bits of the Status Register, as shown in Table 2.
As the above table showing, the summary of the Software Protected Mode (SPM) and Hardware Protected Mode (HPM).
Software Protected Mode (SPM):
-
When SRWD bit=0, no matter WP#/SIO2 is low or high, the WREN instruction may set the WEL bit and can
change the values of SRWD, BP3, BP2, BP1, BP0. The protected area, which is defined by BP3, BP2, BP1,
BP0, is at software protected mode (SPM).
-
When SRWD bit=1 and WP#/SIO2 is high, the WREN instruction may set the WEL bit can change the values of
SRWD, BP3, BP2, BP1, BP0. The protected area, which is defined by BP3, BP2, BP1, BP0, is at software pro-
tected mode (SPM)
Hardware Protected Mode (HPM):
-
When SRWD bit=1, and then WP#/SIO2 is low (or WP#/SIO2 is low before SRWD bit=1), it enters the hardware
protected mode (HPM). The data of the protected area is protected by software protected mode by BP3, BP2,
BP1, BP0 and hardware protected mode by the WP#/SIO2 to against data modification.
Note:
To exit the hardware protected mode requires WP#/SIO2 driving high once the hardware protected mode is entered.
If the WP#/SIO2 pin is permanently connected to high, the hardware protected mode can never be entered; only
can use software protected mode via BP3, BP2, BP1, BP0.
If the system goes into four I/O mode, the feature of HPM will be disabled.
P/N: PM1428
REV. 0.06, MAR. 05, 2009
18
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