Rainbow Electronics AT45DB021D - Manual (Page 13)

13
3638K–DFLASH–11/2012
AT45DB021D
7.1.1 Erase Sector Protection Register Command
In order to modify and change the values of the Sector Protection Register, it must first be erased using the Erase
Sector Protection Register command.
To erase the Sector Protection Register, the CS pin must first be asserted as it would be with any other command.
Once the CS pin has been asserted, the appropriate 4-byte opcode sequence must be clocked into the device via
the SI pin. The 4-byte opcode sequence must start with 3DH and be followed by 2AH, 7FH, and CFH. After the last
bit of the opcode sequence has been clocked in, the CS pin must be deasserted to initiate the internally self-timed
erase cycle. The erasing of the Sector Protection Register should take place in a time of t
PE
, during which time the
Status Register will indicate that the device is busy. If the device is powered-down before the completion of the
erase cycle, then the contents of the Sector Protection Register cannot be guaranteed.
The Sector Protection Register can be erased with the sector protection enabled or disabled. Since the erased
state (FFH) of each byte in the Sector Protection Register is used to indicate that a sector is specified for
protection, leaving the sector protection enabled during the erasing of the register allows the protection scheme to
be more effective in the prevention of accidental programming or erasing of the device. If for some reason an
erroneous program or erase command is sent to the device immediately after erasing the Sector Protection
Register and before the register can be reprogrammed, then the erroneous program or erase command will not be
processed because all sectors would be protected.
Table 7-4. Erase Sector Protection Register Command
Figure 7-2. Erase Sector Protection Register
7.1.2 Program Sector Protection Register Command
Once the Sector Protection Register has been erased, it can be reprogrammed using the Program Sector
Protection Register command.
To program the Sector Protection Register, the CS pin must first be asserted and the appropriate 4-byte opcode
sequence must be clocked into the device via the SI pin. The 4-byte opcode sequence must start with 3DH and be
followed by 2AH, 7FH, and FCH. After the last bit of the opcode sequence has been clocked into the device, the
data for the contents of the Sector Protection Register must be clocked in. As described in
Section 7.1 , the Sector
Protection Register contains 4-bytes of data, so 4-bytes must be clocked into the device. The first byte of data
corresponds to sector zero, the second byte corresponds to sector one, the third byte corresponds to sector two,
and the last byte of data corresponding to sector three.
After the last data byte has been clocked in, the CS pin must be deasserted to initiate the internally self-timed
program cycle. The programming of the Sector Protection Register should take place in a time of t
P
, during which
time the Status Register will indicate that the device is busy. If the device is powered-down during the program
cycle, then the contents of the Sector Protection Register cannot be guaranteed.
If the proper number of data bytes is not clocked in before the CS pin is deasserted, then the protection status of
the sectors corresponding to the bytes not clocked in can not be guaranteed. For example, if only the first two bytes
are clocked in instead of the complete 8-bytes, then the protection status of the last six sectors cannot be
Command Byte 1 Byte 2 Byte 3 Byte 4
Erase Sector Protection Register 3DH 2AH 7FH CFH
Opcode
Byte 1
Opcode
Byte 2
Opcode
Byte 3
Opcode
Byte 4
CS
Each transition
represents 8 bits
SI