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 opera-
tions, the inputs and control levels they require, and the
resulting output. The following subsections describe
each of these operations in further detail.
Table 1. Device Bus Operations
CLK
(See
Operation
CE#
L
OE#
L
WE#
H
Amax–0
Addr In
Addr In
Addr In
Addr In
HIGH Z
HIGH Z
DQ15–0 RESET# Note) AVD#
Asynchronous Read - Addresses Latched
Asynchronous Read - Addresses Steady State
Asynchronous Write
I/O
I/O
H
H
H
H
H
L
X
X
X
L
L
H
L
L
L
H
L
I/O
Synchronous Write
L
H
L
I/O
Standby (CE#)
H
X
X
X
HIGH Z
HIGH Z
X
X
X
X
Hardware Reset
X
X
Burst Read Operations
Load Starting Burst Address
L
L
X
L
H
H
H
H
Addr In
HIGH Z
HIGH Z
HIGH Z
X
H
H
H
L
Advance Burst to next address with
appropriate Data presented on the Data Bus
Burst
Data Out
H
X
X
Terminate current Burst read cycle
H
X
X
X
HIGH Z
HIGH Z
Terminate current Burst read cycle via
RESET#
X
Terminate current Burst read cycle and start
new Burst read cycle
L
X
H
HIGH Z
I/O
H
Legend: L = Logic 0, H = Logic 1, X = Don’t Care, S = Stable Logic 0 or 1 but no transitions.
Note: Default active edge of CLK is the rising edge.
The internal state machine is set for reading array data
in asynchronous mode upon device power-up, or after
a hardware reset. This ensures that no spurious alter-
ation of the memory content occurs during the power
transition.
Requirements for Asynchronous Read
Operation (Non-Burst)
To read data from the memory array, the system must
first assert a valid address on Amax–A0, while driving
AVD# and CE# to V . WE# should remain at V . The
IL
IH
rising edge of AVD# latches the address. The data will
appear on DQ15–DQ0. Since the memory array is
divided into four banks, each bank remains enabled for
read access until the command register contents are
altered.
Requirements for Synchronous (Burst)
Read Operation
The device is capable of continuous sequential burst
operation and linear burst operation of a preset length.
When the device first powers up, it is enabled for asyn-
chronous read operation.
Address access time (t
) is equal to the delay from
ACC
stable addresses to valid output data. The chip enable
Prior to entering burst mode, the system should deter-
mine how many wait states are desired for the initial
access time (t ) is the delay from the stable
CE
addresses and stable CE# to valid data at the outputs.
word (t
) of each burst access, what mode of burst
The output enable access time (t ) is the delay from
IACC
OE
operation is desired, which edge of the clock will be the
the falling edge of OE# to valid data at the output.
May 10, 2006 27024B3
Am29BDS128H/Am29BDS640H
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