AM29F400AT datasheet(11/35 Pages) AMD

11 / 35 page

Am29F400AT/Am29F400AB

PRELIMINARY

It is possible to determine if a sector is protected in the

system by writing an Autoselect command. Performing

a read operation at the address location XX02H, where

the higher order address bits A12–A17 is the desired

sector address, will produce a logical “1” at DQ0 for a

protected sector. See Table 3 for Autoselect codes.

Temporary Sector Unprotect

This feature allows temporary unprotection of previ-

ously protected sectors of the Am29F400A device in

order to change data in-system. The Sector Unprotect

mode is activated by setting the RESET pin to high volt-

age (12V). During this mode, formerly protected sec-

tors can be programmed or erased by selecting the

sector addresses. Once the 12 V is taken away from

the RESET pin, all the previously protected sectors will

be protected again. Refer to Figures 16 and 17.

Command Deﬁnitions

Device operations are selected by writing speciﬁc ad-

dress and data sequences into the command register.

Writing incorrect address and data values

or writing them in the improper sequence will reset

the device to the read mode. Table 7 deﬁnes the valid

Erase Suspend (B0H) and Erase Resume (30H) com-

mands are valid only while the Sector Erase operation

is in progress. Moreover, both Reset/Read commands

are functionally equivalent, resetting the device to the

read mode.

AM29F400AT 数据表(PDF) 11 Page - Advanced Micro Devices