AT25SF041 Datasheet, PDF (25/46 Pages) List of Unclassifed Manufacturers – 4-Mbit, 2.5V Minimum SPI Serial Flash Memory with Dual-I/O and Quad-I/O Support

10.1.3 WEL Bit
The WEL bit indicates the current status of the internal Write Enable Latch. When the WEL bit is in the logical “0” state,
the device will not accept any Byte/Page Program, erase, Program Security Register, Erase Security Register, or Write
Status Register commands. The WEL bit defaults to the logical “0” state after a device power-up or reset operation. In
addition, the WEL bit will be reset to the logical “0” state automatically under the following conditions:
 Write Disable operation completes successfully
 Write Status Register operation completes successfully or aborts
 Program Security Register operation completes successfully or aborts
 Erase Security Register operation completes successfully or aborts
 Byte/Page Program operation completes successfully or aborts
 Block Erase operation completes successfully or aborts
 Chip Erase operation completes successfully or aborts
If the WEL bit is in the logical “1” state, it will not be reset to a logical “0” if an operation aborts due to an incomplete or
unrecognized opcode being clocked into the device before the CS pin is deasserted. In order for the WEL bit to be reset
when an operation aborts prematurely, the entire opcode for a Byte/Page Program, erase, Program Security Register,
Erase Security Register, or Write Status Register command must have been clocked into the device.
10.1.4 RDY/BSY Bit
The RDY/BSY bit is used to determine whether or not an internal operation, such as a program or erase, is in progress.
To poll the RDY/BSY bit to detect the completion of a program or erase cycle, new Status Register data must be
continually clocked out of the device until the state of the RDY/BSY bit changes from a logical “1” to a logical “0”.
10.1.5 LB3, LB2, LB1 Bits
The LB3, LB2, and LB1 bits are used to determine if any of the three Security Register pages are locked. 
The LB3 bit is in the logical “1” state if Security Register page-2 is locked and cannot be erased or programmed.
The LB2 bit is in the logical “1” state if Security Register page-1 is locked and cannot be erased or programmed
The LB1 bit is in the logical “1” state if Security Register page-0 is locked and cannot be erased or programmed.
10.1.6 QE Bit
The QE bit is used to determine if the device is in the Quad Enabled mode. If the QE bit is in the logical “1” state, then the
HOLD and WP pins functions as input/output pins similar to the SI and SO. If the QE bit is in the logical “0” state, then the
HOLD pin functions as an input only and the WP pin functions as an input only.
10.2
Write Status Register (01h)
The Write Status Register command is used to modify the Block Protection, Security Register Lock-down, Quad Enable,
and Status Register Protection. Before the Write Status Register 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 Write Status Register command, the CS pin must first be asserted and the opcode of 01h must be clocked
into the device followed by one or two bytes of data. The first byte of data consists of the SRP0, SEC, TB, BP2, BP1, BP0
bit values and 2 dummy bits. The second byte is optional and consists of 1 dummy bit, the CMP, LB3, LB2, LB1, 1
dummy bit, the QE, and 1 dummy bit. When the CS pin is deasserted, the bit values in the Status Register will be
modified, and the WEL bit in the Status Register will be reset back to a logical “0”.
The complete one byte or two bytes of data must be clocked into the device before the CS pin is deasserted, and the CS
pin must be deasserted on even byte boundaries (multiples of eight bits); otherwise, the device will abort the operation,
the state of the Status Register bits will not change, memory protection status will not change, and the WEL bit in the
Status Register will be reset back to the logical “0” state
AT25SF041 25
DS-25SF041–044C–7/2014