D A T A
S H E E T
DEVICE BUS OPERATIONS
This section describes the requirements and use of the
device bus operations, which are initiated through the
internal command register. The command register
itself does not occupy any addressable memory loca-
tion. The register is composed of latches that store the
commands, along with the address and data informa-
tion needed to execute the command. The contents of
the register serve as inputs to the internal state
machine. The state machine outputs dictate the func-
tion of the device. Table 1 lists the device bus
operations, the inputs and control levels they require,
and the resulting output. The following subsections
describe each of these operations in further detail.
Table 1.
Operation
Read
Write
Standby
Output Disable
Reset
Sector Protect (Note 2)
Sector Unprotect (Note 2)
Temporary Sector Unprotect
CE#
L
L
V
CC
±
0.3 V
L
X
L
L
X
Am29LV040B Device Bus Operations
OE#
L
H
X
H
X
H
H
X
WE#
H
L
X
H
X
L
L
X
Addresses (Note 1)
A
IN
A
IN
X
X
X
Sector Address, A6 = L, A1 = H, A0 = L
Sector Address, A6 = H, A1 = H, A0 = L
A
IN
DQ0–DQ7
D
OUT
D
IN
High-Z
High-Z
High-Z
D
IN
, D
OUT
D
IN
, D
OUT
D
IN
Legend:
L = Logic Low = V
IL
, H = Logic High = V
IH
, V
ID
= 12.0
±
0.5 V, X = Don’t Care, A
IN
= Address In, D
IN
= Data In, D
OUT
= Data Out
Notes:
1. Addresses are A18–A0.
2. The sector protect and sector unprotect functions may also be implemented via programming equipment. See the “Sector
Protection/Unprotection” section.
Requirements for Reading Array Data
To read array data from the outputs, the system must
drive the CE# and OE# pins to V
IL
. CE# is the power
control and selects the device. OE# is the output
control and gates array data to the output pins. WE#
should remain at V
IH
.
The internal state machine is set for reading array data
upon device power-up, or after a hardware reset. This
ensures that no spurious alteration of the memory
content occurs during the power transition. No
command is necessary in this mode to obtain array
data. Standard microprocessor read cycles that assert
valid addresses on the device address inputs produce
valid data on the device data outputs. The device
remains enabled for read access until the command
register contents are altered.
See “Reading Array Data” for more information. Refer
to the AC Read Operations table for timing specifica-
tions and to Figure 11 for the timing diagram. I
CC1
in the
DC Characteristics table represents the active current
specification for reading array data.
Writing Commands/Command Sequences
To write a command or command sequence (which
includes programming data to the device and erasing
sectors of memory), the system must drive WE# and
CE# to V
IL
, and OE# to V
IH
.
The device features an
Unlock Bypass
mode to facili-
tate faster programming. Once the device enters the
Unlock Bypass mode, only two write cycles are
required to program a byte, instead of four. The “Byte
programming data to the device using both standard
and Unlock Bypass command sequences.
An erase operation can erase one sector, multiple sec-
tors, or the entire device. Table 2 indicates the address
space that each sector occupies. A “sector address”
consists of the address bits required to uniquely select
a sector. The “Command Definitions” section has
details on erasing a sector or the entire chip, or sus-
pending/resuming the erase operation.
After the system writes the autoselect command
sequence, the device enters the autoselect mode. The
system can then read autoselect codes from the
internal register (which is separate from the memory
array) on DQ7–DQ0. Standard read cycle timings apply
10
Am29LV040B
21354E4 October 11, 2006
AMD [ ADVANCED MICRO DEVICES ]
