12
Am29F800T/Am29F800B
8/18/97
P R E L I M I N A R Y
Write
Device erasure and programming are accomplished
via the command register. The contents of the register
serve as inputs to the internal state machine. The state
machine outputs dictate the function of the device.
The command register itself does not occupy any ad-
dressable memory location. The register is a latch used
to store the commands, along with the address and
data information needed to execute the command. The
command register is written to by bringing WE to V
IL
,
while CE is at V
IL
and OE is at V
IH
. Addresses are
latched on the falling edge of WE or CE, whichever
happens later; while data is latched on the rising edge
of WE or CE, whichever happens first. Standard micro-
processor write timings are used.
Refer to AC Write Characteristics and the Erase/Pro-
gramming Waveforms for specific timing parameters.
Sector Protection
The Am29F800 features hardware sector protection.
This feature will disable both program and erase oper-
ations in any combination of nineteen sectors of mem-
ory. The sector protect feature is enabled using
programmingequipment at the user’s site The device
is shipped with all sectors unprotected. Alternatively,
AMD may program and protect sectors in the factory
prior to shipping the device (AMD’s ExpressFlash
Service).
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–A18 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 Am29F800 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 17 and 18.
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 writ-
ing them in the improper sequence will reset the
device to the read mode.
Table 7 defines the valid
register command sequences. Note that the Erase
Suspend (B0H) and Erase Resume (30H) commands
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.