11.2.8 Write Status Register (01h)
The Write Status Register instruction allows the Status Register to be written. A Write Enable
instruction must previously have been executed for the device to accept the Write Status Register
Instruction (Status Register bit WEL must equal 1). Once write is enabled, the instruction is entered
by driving /CS low, sending the instruction code “01h”, and then writing the status register data byte
or word as illustrated in figure 8. The Status Register bits are shown in figure 3 and described
earlier in this datasheet.
Only non-volatile Status Register bits SRP0, SEC, TB, BP2, BP1, BP0 (bits 7, 5, 4, 3, 2 of Status
Register-1) and QE, SRP1 (bits 9 and 8 of Status Register-2) can be written to. All other Status
Register bit locations are read-only and will not be affected by the Write Status Register instruction.
The /CS pin must be driven high after the eighth or sixteenth bit of data that is clocked in. If this is
not done the Write Status Register instruction will not be executed. If /CS is driven high after the
eighth clock, the QE and SRP1 bits will be cleared to 0. After /CS is driven high, the self-timed
Write Status Register cycle will commence for a time duration of tw (See AC Characteristics). While
the Write Status Register cycle is in progress, the Read Status Register instruction may still be
accessed to check the status of the BUSY bit. The BUSY bit is a 1 during the Write Status Register
cycle and a 0 when the cycle is finished and ready to accept other instructions again. After the
Write Status Register cycle has finished, The Write Enable Latch (WEL) bit in Status Register will
be cleared to 0.
The Write Status Register instruction allows the Block Protect bits (SEC, TB, BP2, BP1 and BP0)
to be set for protecting all, a portion, or none of the memory from erase and program instructions.
Protected areas become read-only (see Status Register Memory Protection table and description).
The Write Status Register instruction also allows the Status Register Protect bits (SRP0, SRP1) to
be set. Those bits are used in conjunction with the Write protect (/WP) pin, Lock out or OTP
features to disable writes to the status register. Please refer to 11.1.16 for detailed descriptions
Status Register protection methods. Factory default all Status Register bits are 0.
CLK Mode 0
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 Mode 3
Status Register1 In
Status Register2 In
76 5 4 3 2 X XXX X XX X 9 8
Figure 8. Write Status Register Instruction Sequence Diagram