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May 8, 2006 25692A2
Am29BDS643G
21
D A T A S H E E T
Table 9.
Wait States for Handshaking
* In the 8-, 16- and 32-word burst read modes, the address
pointer does not cross 64-word boundaries (addresses
which are multiples of 3Eh).
The autoselect function allows the host system to
determine whether the flash device is enabled for
handshaking. See the “Autoselect Command
Sequence” section for more information.
Enable PS (Power Saving) Mode
Command Sequence
The Enable PS (Power Saving) Mode command
sequence is required to set the device to the PS mode.
On power up, the Power Saving mode is disabled. The
command sequence consists of two unlock cycles fol-
lowed by a command cycle in which the address and
data should 555h/70h, respectively. The PS mode
remains enabled until the device is hardware reset
(either device is powered down or RESET# is asserted
low).
Sector Lock/Unlock Command Sequence
The sector lock/unlock command sequence allows the
system to determine which sectors are protected from
accidental writes. When the device is first powered up,
all sectors are locked. To unlock a sector, the system
must write the sector lock/unlock command sequence.
Two cycles are first written: addresses are don’t care
and data is 60h. During the third cycle, the sector
address (SLA) and unlock command (60h) is written,
while specifying with address A6 whether that sector
should be locked (A6 = V
IL
) or unlocked (A6 = V
IH
).
After the third cycle, the system can continue to lock or
unlock additional cycles, or exit the sequence by writing
F0h (reset command).
Note that the last two outermost boot sectors can be
locked by taking the WP# signal to V
IL
. Also, if V
PP
is at
V
IL
all sectors are locked; if the V
PP
input is at V
PP
, all
sectors are unlocked.
Reset Command
Writing the reset command resets the banks to the
read or erase-suspend-read mode. Address bits are
don’t cares for this command.
The reset command may be written between the
sequence cycles in an erase command sequence
before erasing begins. This resets the bank to which
the system was writing to the read mode. Once erasure
begins, however, the device ignores reset commands
until the operation is complete.
The reset command may be written between the
sequence cycles in a program command sequence
before programming begins. This resets the bank to
which the system was writing to the read mode. If the
program command sequence is written to a bank that
is in the Erase Suspend mode, writing the reset
command returns that bank to the erase-suspend-read
mode. Once programming begins, however, the device
ignores reset commands until the operation is com-
plete.
The reset command may be written between the
sequence cycles in an autoselect command sequence.
Once in the autoselect mode, the reset command must
be written to return to the read mode. If a bank entered
the autoselect mode while in the Erase Suspend mode,
writing the reset command returns that bank to the
erase-suspend-read mode.
If DQ5 goes high during a program or erase operation,
writing the reset command returns the banks to the
read mode (or erase-suspend-read mode if that bank
was in Erase Suspend).
Autoselect Command Sequence
The autoselect command sequence allows the host
system to access the manufacturer and device codes,
and determine whether or not a sector is protected.
Table 10 shows the address and data requirements.
The autoselect command sequence may be written to
an address within a bank that is either in the read or
erase-suspend-read mode. The autoselect command
may not be written while the device is actively program-
ming or erasing in the other bank.
The autoselect command sequence is initiated by first
writing two unlock cycles. This is followed by a third
write cycle that contains the bank address and the
autoselect command. The bank then enters the
autoselect mode. The system may read at any address
within the same bank any number of times without ini-
tiating another autoselect command sequence. The fol-
lowing table describes the address requirements for
the various autoselect functions, and the resulting data.
BA represents the bank address, and SA represents
Conditions at Address
Typical No. of Clock
Cycles after AVD# Low
40 MHz
54/66 MHz
Initial address is even
4
5
Initial address is odd
5
6
Initial address is even,
and is at boundary crossing*
6
7
Initial address is odd,
and is at boundary crossing*
7
8