M25P64
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
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
Table 7. Protection Modes
W
Signal
1
0
1
SRWD
Bit
0
0
1
Software
Protected
(SPM)
Mode
Write Protection of the
Status Register
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
Status Register is
Hardware write protected
The values in the SRWD,
BP2, BP1 and BP0 bits
cannot be changed
Memory Content
Protected Area
1
Unprotected Area
1
(whose duration is t
W
) 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 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
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.
Protected against Page
Program, Sector Erase
and Bulk Erase
Ready to accept Page
Program and Sector Erase
instructions
0
1
Hardware
Protected
(HPM)
Protected against Page
Program, Sector Erase
and Bulk Erase
Ready to accept Page
Program and Sector Erase
instructions
Note: 1. As defined by the values in the Block Protect (BP2, BP1, BP0) bits of the Status Register, as shown in
The protection features of the device are summa-
rized in
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 Latch (WEL) bit has
previously been set by a Write Enable (WREN) in-
struction, regardless of the whether Write Protect
(W) is driven High or Low.
When the Status Register Write Disable (SRWD)
bit of the Status Register is set to 1, two cases
need to be considered, depending on the state of
Write Protect (W):
– If Write Protect (W) is driven High, it is
possible to write to the Status Register
provided that the Write Enable Latch (WEL) bit
has previously been set by a Write Enable
(WREN) instruction.
– If Write Protect (W) is driven Low, it is
not
possible to write to the Status Register
even
if
the Write Enable Latch (WEL) bit has
previously been set by a Write Enable
(WREN) instruction. (Attempts to write to the
Status Register are rejected, and are not
accepted for execution). As a consequence,
all the data bytes in the memory area that are
software protected (SPM) by the Block Protect
(BP2, BP1, BP0) bits of the Status Register,
are also hardware protected against data
modification.
Regardless of the order of the two events, the
Hardware Protected Mode (HPM) can be entered:
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STMICROELECTRONICS [ STMICROELECTRONICS ]
