March 8, 2002 Am49DL640BG 25
PRELIMINARY
FLASH COMMAND DEFINITIONS
Writing specific address and data commands or se-
quences int o the command register initi ates device op-
erations. Table 12 defines the valid register command
sequenc es. Writing i n correct add ress an d data val -
ues or writing them in the improper sequence re sets
the device to reading array data.
All a ddre sses are l atc hed o n th e falli ng edge of WE#
or CE#f, whichever happens later. All data is latched
on the risin g edge of WE # or CE#f, which ever hap -
pens first. Refer to t he pS RAM AC Character istics
section for timing diagrams.
Reading Array Data
The device is automatically set to reading array data
after device pow er-up. No co mma nds are requir ed t o
retrieve data. Each bank is ready to read array data
after completing an Embedded Program or Em bedded
Erase algorithm.
After the device accepts an Erase Suspend co mmand,
the corresponding bank enters the erase-sus-
pend-read mode, after which the system can read
data from any no n-erase-suspended sector wit hin the
same bank. The system can read array data using the
stand ard rea d ti ming , e xcept tha t if it r ead s at an ad-
dress within erase-suspended sectors, the device out-
puts status data. After completing a programming
operation in the Erase Suspend mode, the system
may once again read array data with the same excep-
tion. See the Erase Suspend/Erase Resume Com-
mands section for more information.
The system must issue the reset command to return a
bank to the read (or erase-suspend- read) mode if DQ5
goes high during an active program or erase opera-
tion, o r if the bank is in the autosele ct mod e. S ee the
next section, Reset Command, for more information.
See also Requirements for Reading A rray Data in the
section for more information. The Flash Read-Only
Operations table provides the read parameters, and
Figure 14 shows the timing diagram.
Reset Command
Writing the reset command resets the banks to the
read or erase-suspend-read mode. A ddress bits are
don’t cares for this command.
The reset command may be written between the se-
quence cycles in an erase command sequence before
erasing begins. This resets the bank t o which the sys-
tem was writing to the read mode. Once erasure be-
gins, however, the device ignores reset commands
until th e operation is complete.
The reset command may be written between the
seque nce cycles in a pro gram com mand sequenc e
before programming begins. This resets the bank to
which the s ystem was writing t o the read mode. If the
progra m command sequen ce is writte n to a bank that
is in the Erase Suspend mode, writing the reset
command returns that bank to the erase-sus-
pend-read mode. Once programming begins, how-
ever, the device ignores reset commands until the
operation is complete.
The reset command may be written between the se-
quence cycles in an autoselect command sequence.
Once in the autoselect mode, the reset command
mus t be w ritten t o return t o the read m ode. If a b ank
entered the autoselect mode while in the Erase Sus-
pend mo de, writing the res et command returns that
bank to the erase-suspend-read mode.
If DQ5 goes high during a program or er ase op eration,
writing t he reset comman d returns the banks to the
read mode (or eras e-sus pend-read mode if that bank
was in Erase Suspend) .
Autoselect Command Sequence
The autoselect command sequence allows the hos t
system to access the manufacturer and device codes,
and determine whether or not a sector is protected.
The autoselect command sequence may be written to
an address within a bank that is either in the read or
eras e-sus pend-r ead m ode. The au tose lect c ommand
ma y not be wr itten wh ile the device is active ly pro-
gramming or erasing in the other bank.
The autoselect command sequence is initiated by first
writing two unlock cycl es. This is followed by a third
write cycle that contains the bank address and the au-
to select comma nd. Th e b ank the n ent ers t he autos e-
lect mode. The system may read any number of
autoselect codes without r einitiating the command se-
quence.
Table 12 shows the address and data requirements.
To determine sector protection information, the system
must write to the appropriate bank address (BA) and
sector address (SADD). Tab le 3 s hows the address
range and bank number as sociated with each sector.
The system must write the reset command to ret ur n to
the read mode (or erase-suspend-read mode if the
bank was previousl y in Erase Suspend).
Ente r SecSi™ Sector/Exit SecSi Sector
Command Sequenc e
The SecSi Sector regi on pr ovi des a secured dat a ar ea
containing a random, sixteen-byte electronic serial
number (ESN). The system can access the SecSi
Se ctor r egion by issuin g the th ree- cycle Enter SecSi
Sector command sequence. The device continues to
access the S ecSi Sector reg ion until the s ystem is-
sues the four-cycle Exit SecSi Sector command se-
