ACE25C400

4MB Serial Flash Memory

VER 1.2

7

HOLD# operation to avoid resetting the internal logic state of the device.

Figure 3 Hold condition waveform

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

ACE25C400 provides several means to protect the data from inadvertent writes.

Write Protect Features



Device resets when VCC is below threshold



Time delay write disable after Power-up



Write enable/disable instructions and automatic write disable after erase or program



Software and Hardware (WP# pin) write protection using Status Register



Write Protection using Power-down instruction



Lock Down write protection for Status Register until the next power -up



One Time Program (OTP) write protection for array and Security Sectors using Status Register.

Upon power-up or at power-down, the ACE25C400 will maintain a reset condition while VCC is

below the threshold value of VWI, (See “12.3 Power-up Timing” and Figure 23). While reset, all

operations are disabled and no instructions are recognized. During power-up and after the VCC

voltage exceeds VWI, all program and erase related instructions are further disabled for a time delay

the Write Status Register instructions. Note that the chip select pin (CS#) must track the VCC supply

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, Block Erase, Chip Erase or Write Status Register instr uction 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 inst ruction and

setting the Status Register Protect (SRP) and Block Protect (BP2, BP1 and BP0) bits. These settings

allow a portion as small as a 4KB sector or the entire memory array to be configured as read only.

Used in conjunction with the Write Protect (W P#) pin, changes to the Status Register can be enabled

or disabled under hardware control. See Status Register section for further information. Additionally,

the Power-down instruction offers an extra level of write protection as all instructions are ignor ed

except for the Release Power-down instruction.