Rainbow Electronics W25X64 - Manual (Page 11)

W25X16, W25X32, W25X64
Publication Release Date: June 28, 2006
- 11 - Preliminary - Revision B
10.2 WRITE PROTECTION
Applications that use non-volatile memory must take into consideration the possibility of noise and
other adverse system conditions that may compromise data integrity. To address this concern the
W25X16/32/64 provides several means to protect data from inadvertent writes.
10.2.1 Write Protect Features
• Device resets when VCC is below threshold.
• Time delay write disable after Power-up.
• Write enable/disable instructions.
• Automatic write disable after program and erase.
• Software write protection using Status Register.
• Hardware write protection using Status Register and /WP pin.
• Write Protection using Power-down instruction.
Upon power-up or at power-down the W25X16/32/64 will maintain a reset condition while VCC is
below the threshold value of V
WI , (See Power-up Timing and Voltage Levels and Figure 20). While
reset, all operations are disabled and no instructions are recognized. During power-up and after the
VCC voltage exceeds V
WI , all program and erase related instructions are further disabled for a time
delay of t PUW . This includes the Write Enable, Page Program, Sector Erase, Block Erase, Chip Erase
and the Write Status Register instructions. Note that the chip select pin (/CS) must track the VCC
supply level at power-up until the VCC-min level and t
VSL time delay is reached. If needed a pull-up
resister on /CS can be used to accomplish this.
After power-up the device is automatically placed in a write-disabled state with the Status Register
Write Enable Latch (WEL) set to a 0. A Write Enable instruction must be issued before a Page
Program, Sector Erase, Chip Erase or Write Status Register instruction will be accepted. After
completing a program, erase or write instruction the Write Enable Latch (WEL) is automatically
cleared to a write-disabled state of 0.
Software controlled write protection is facilitated using the Write Status Register instruction and setting
the Status Register Protect (SRP) and Block Protect (TB, BP2, BP1, and BP0) bits. These Status
Register bits allow a portion or all of the memory to be configured as read only. Used in conjunction
with the Write Protect (/WP) pin, changes to the Status Register can be enabled or disabled under
hardware control. See Status Register for further information.
Additionally, the Power-down instruction offers an extra level of write protection as all instructions are
ignored except for the Release Power-down instruction.