Datasheet

 2003-2011 Microchip Technology Inc. DS21831E-page 11
25AA128/25LC128
2.6 Write Status Register (WRSR)
The Write Status Register (WRSR) instruction allows the
user to write to the nonvolatile bits in the STATUS reg-
ister as shown in Table 2-2. The user is able to select
one of four levels of protection for the array by writing
to the appropriate bits in the STATUS register. The
array is divided up into four segments. The user has the
ability to write-protect none, one, two, or all four of the
segments of the array. The partitioning is controlled as
shown in Table 2-3.
The Write-Protect Enable (WPEN) bit is a nonvolatile
bit that is available as an enable bit for the WP
pin. The
Write-Protect (WP
) pin and the Write-Protect Enable
(WPEN) bit in the STATUS register control the
programmable hardware write-protect feature. Hard-
ware write protection is enabled when WP
pin is low
and the WPEN bit is high. Hardware write protection is
disabled when either the WP
pin is high or the WPEN
bit is low. When the chip is hardware write-protected,
only writes to nonvolatile bits in the STATUS register
are disabled. See Table 2-4 for a matrix of functionality
on the WPEN bit.
See Figure 2-7 for the WRSR timing sequence.
TABLE 2-3: ARRAY PROTECTION
FIGURE 2-7: WRITE STATUS REGISTER TIMING SEQUENCE (WRSR)
BP1 BP0
Array Addresses
Write-Protected
00
none
01
upper 1/4
(3000h-3FFFh)
10
upper 1/2
(2000h-3FFFh)
11
all
(0000h-3FFFh)
SO
SI
CS
9101112131415
01000000
7654
210
Instruction Data to STATUS Register
High-Impedance
SCK
0 23456718
3
Note: An internal write cycle (TWC) is initiated on the rising edge of CS after a valid write STATUS register