Instructions
M95040-125, M95020-125, M95010-125
Doc ID 022545 Rev 1
6.4
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.
The Write Status Register (WRSR) instruction is entered by driving Chip Select (S) low,
sending the instruction code followed by the data byte on Serial Data input (D), and driving
the Chip Select (S) signal high. 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.
Driving the Chip Select (S) signal high at a byte boundary of the input data triggers the self-
timed write cycle that takes t
W
to complete (as specified in AC tables under
). The instruction sequence is shown in
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 WIP bit is 1 during the self-timed write
cycle t
W
, and, 0 when the write cycle is complete. The WEL bit (Write enable latch) is also
reset at the end of the write cycle t
W
.
The Write Status Register (WRSR) instruction allows the user to change the values of the
BP1, BP0 bits which define the size of the area that is to be treated as read only, as defined
in
Table 2: Write-protected block size
The contents of the BP1, BP0 bits are updated after the completion of the WRSR
instruction, including the t
W
write cycle.
The Write Status Register (WRSR) instruction has no effect on the b7, b6, b5, b4, b1 and b0
bits in the Status register. Bits b7, b6, b5, b4 are always read as 0.
Figure 10.
Write Status Register (WRSR) sequence
The instruction is not accepted, and is not executed, under the following conditions:
●
if the Write Enable Latch (WEL) bit has not been set to 1 (by executing a Write Enable
instruction just before)
●
if a write cycle is already in progress
●
if the device has not been deselected, by Chip Select (S) being driven high, after the
eighth bit, b0, of the data byte has been latched in
●
if Write Protect (W) is low during the WRSR command (instruction, address and data)
C
D
AI01445B
S
Q
2
1
3
4
5
6
7
8
9 10 11 12 13 14 15
High Impedance
Instruction
Status
Register In
0
7
6
5
4
3
2
0
1
MSB
Obsolete Product(s) - Obsolete Product(s)
