AT25DF041A-MU ATMEL [ATMEL Corporation], AT25DF041A-MU Datasheet - Page 20

• Manufacturer Part Number: AT25DF041A-MU
• Description: 4-megabit 2.7-volt Only Serial Firmware DataFlash Memory
• Manufacturer: ATMEL [ATMEL Corporation]

9.6
20
Read Sector Protection Registers
AT25DF041A
If the desire is to only change the SPRL bit without performing a Global Protect or Global Unpro-
tect, then the system can simply write a 0Fh to the Status Register to change the SPRL bit from
a logical “1” to a logical “0” provided the WP pin is deasserted. Likewise, the system can write an
F0h to change the SPRL bit from a logical “0” to a logical “1” without affecting the current sector
protection status (no changes will be made to the Sector Protection Registers).
When writing to the Status Register, bits 5, 4, 3, and 2 will not actually be modified but will be
decoded by the device for the purposes of the Global Protect and Global Unprotect functions.
Only bit 7, the SPRL bit, will actually be modified. Therefore, when reading the Status Register,
bits 5, 4, 3, and 2 will not reflect the values written to them but will instead indicate the status of
the WP pin and the sector protection status. Please refer to the “Read Status Register” section
and
read for bits 5, 4, 3, and 2.
The Sector Protection Registers can be read to determine the current software protection status
of each sector. Reading the Sector Protection Registers, however, will not determine the status
of the WP pin.
To read the Sector Protection Register for a particular sector, the CS pin must first be asserted
and the opcode of 3Ch must be clocked in. Once the opcode has been clocked in, three address
bytes designating any address within the sector must be clocked in. After the last address byte
has been clocked in, the device will begin outputting data on the SO pin during every subse-
quent clock cycle. The data being output will be a repeating byte of either FFh or 00h to denote
the value of the appropriate Sector Protection Register.
Table 9-3.
Deasserting the CS pin will terminate the read operation and put the SO pin into a high-imped-
ance state. The CS pin can be deasserted at any time and does not require that a full byte of
data be read.
In addition to reading the individual Sector Protection Registers, the Software Protection Status
(SWP) bit in the Status Register can be read to determine if all, some, or none of the sectors are
software protected (refer to the
Figure 9-5.
SCK
SO
CS
Output Data
SI
Table 10-1 on page 23
00h
FFh
Read Sector Protection Register – Output Data
Read Sector Protection Register
MSB
HIGH-IMPEDANCE
0
0
Sector Protection Register Value
Sector Protection Register value is 0 (sector is unprotected).
Sector Protection Register value is 1 (sector is protected).
0
1
1
2
OPCODE
1
3
1
4
for details on the Status Register format and what values can be
1
5
“Status Register Commands” on page 23
0
6
0
7
MSB
A
8
A
9
ADDRESS BITS A23-A0
A
10 11
A
A
12
A
A
29 30
A
A
31 32
MSB
D
D
33
DATA BYTE
D
34
D
35
for more details).
D
36
D
37 38
3668A–DFLASH–03/07
D
D
39 40
MSB
D
D