Rainbow Electronics AT25DF041A - Manual (Page 16)

16
3668E–DFLASH–11/2012
AT25DF041A
Figure 9-2. Write Disable
9.3 Protect Sector
Every physical sector of the device has a corresponding single-bit Sector Protection Register
that is used to control the software protection of a sector. Upon device power-up or after a
device reset, each Sector Protection Register will default to the logical “1” state indicating that all
sectors are protected and cannot be programmed or erased.
Issuing the Protect Sector command to a particular sector address will set the corresponding
Sector Protection Register to the logical “1” state. The following table outlines the two states of
the Sector Protection Registers.
Before the Protect Sector command can be issued, the Write Enable command must have been
previously issued to set the WEL bit in the Status Register to a logical “1”. To issue the Protect
Sector command, the CS pin must first be asserted and the opcode of 36h must be clocked into
the device followed by three address bytes designating any address within the sector to be
locked. Any additional data clocked into the device will be ignored. When the CS pin is deas-
serted, the Sector Protection Register corresponding to the physical sector addressed by
A23 - A0 will be set to the logical “1” state, and the sector itself will then be protected from
program and erase operations. In addition, the WEL bit in the Status Register will be reset back
to the logical “0” state.
The complete three address bytes must be clocked into the device before the CS pin is deas-
serted, and the CS pin must be deasserted on an even byte boundary (multiples of eight bits);
otherwise, the device will abort the operation, the state of the Sector Protection Register will be
unchanged, and the WEL bit in the Status Register will be reset to a logical “0”.
As a safeguard against accidental or erroneous protecting or unprotecting of sectors, the Sector
Protection Registers can themselves be locked from updates by using the SPRL (Sector Protec-
tion Registers Locked) bit of the Status Register (please refer to the Status Register description
for more details). If the Sector Protection Registers are locked, then any attempts to issue the
Protect Sector command will be ignored, and the device will reset the WEL bit in the Status Reg-
ister back to a logical “0” and return to the idle state once the CS pin has been deasserted.
SCK
CS
SI
SO
MSB
2 3 1 0
0 0 0 0 0 1 0 0
6 7 5 4
OPCODE
HIGH-IMPEDANCE
Table 9-1. Sector Protection Register Values
Value Sector Protection Status
0 Sector is unprotected and can be programmed and erased.
1 Sector is protected and cannot be programmed or erased. This is the default state.