
November 1, 2006  21445E5
Am29F040B
7
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 it-
self does not occupy any addressable memory 
location. The register is composed of latches that store 
the commands, along with the address and data infor-
mation needed to execute the command. The contents 
of the register serve as inputs to the internal state ma-
chine. The state machine outputs dictate the function of 
the device. The appropriate device bus operations 
table lists the inputs and control levels required, and the 
resulting output. The following subsections describe 
each of these operations in further detail.
Table 1. Am29F040B Device Bus Operations
Legend:
L = Logic Low = V
IL
, H = Logic High = V
IH
, V
ID
 = 12.0 
± 
0.5 V, X = Don’t Care, D
IN
 = Data In, D
OUT
 = Data Out, A
IN
 = Address In
Note: 
See the “Sector Protection/Unprotection” section. for more information.
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 con-
trol 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 con-
tent 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 the Read Operations Timings diagram for 
the timing waveforms. 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 in-
cludes 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
.
An erase operation can erase one sector, multiple sec-
tors, or the entire device. The Sector Address Tables 
indicate the address space that each sector occupies. 
A “sector address” consists of the address bits required 
to uniquely select a sector. See the 
“Command Defini-
tions”
 section for details on erasing a sector or the 
entire chip, or suspending/resuming the erase 
operation.
After the system writes the autoselect command se-
quence, the device enters the autoselect mode. The 
system can then read autoselect codes from the inter-
nal register (which is separate from the memory array) 
on DQ7–DQ0. Standard read cycle timings apply in this 
mode. Refer to the 
“Autoselect Mode”
 and 
“Autoselect 
Command Sequence”
 sections for more information.
I
CC2
 in the DC Characteristics table represents the ac-
tive current specification for the write mode. The “AC 
Characteristics” section contains timing specification 
tables and timing diagrams for write operations.
Program and Erase Operation Status
During an erase or program operation, the system may 
check the status of the operation by reading the status 
bits on DQ7–DQ0. Standard read cycle timings and I
CC
read specifications apply. Refer to 
“Write Operation 
Status”
 for more information, and to each AC Charac-
teristics section for timing diagrams.
Standby Mode
When the system is not reading or writing to the device, 
it can place the device in the standby mode. In this 
mode, current consumption is greatly reduced, and the 
Operation
CE#
OE#
WE#
A0–A20
DQ0–DQ7
Read
L
L
H
A
IN
D
OUT
Write
L
H
L
A
IN
D
IN
CMOS Standby
V
CC
 ± 0.5 V
X
X
X
High-Z
TTL Standby
H
X
X
X
High-Z
Output Disable
L
H
H
X
High-Z