AM29F004B datasheet(14/37 Pages) AMD

14 / 37 page

Am29F004B

8/5/05

AD VA NC E

IN FO RM AT ION

Temporary Sector Unprotect

This feature allows temporary unprotection of previously pro-

tected sectors to change data in-system. The Sector

Unprotect mode is activated by setting the OE# pin to 12.0

Volts (VID). Figure 2 shows the algorithm, and Figure 16, on

page 28 and Figure 17, on page 28 show the timing dia-

grams, for this feature. While OE# is at VID, the sector unlock

sequence is written to the device. After the sector unlock

sequence is written, the OE# pin is taken back to VIH. The

device is now in the temporary sector unprotect mode.

While in this mode, formerly protected sectors can be pro-

grammed or erased by selecting the appropriate sector

address during programming or erase operations. Either

sector erase or chip erase operations can be performed in

this mode. Byte program operations require only two cycles,

while sector and chip erase operations only require four

cycles. Refer to the Command Definitions table.

Exiting the temporary sector unprotect mode is accomplished

by either removing VCC from the device or by taking OE#

back to VID and writing the sector relock sequence.

After writing the sector relock sequence, the OE# pin is taken

back to VIH and all previously protected sectors are protected

again.

Figure 2.

Temporary Sector Unprotect Operation

Write the three-cycle

Unlock sequence with com-

mand 20h (Figure 16)

Perform Erase or

Program Operations

OE# = VIH

Temporary Sector

Unprotect

Completed (Note 2)

OE# = VIH (Note 1)

Notes:

All protected sectors unprotected.

All previously protected sectors are protected once again.

START

OE# = VID

Write the two-cycle

Sector Relock sequence (Fig-

ure 17)

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