P r e l i m i n a r y
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 location. The register is com-
posed of latches that store the commands, along with the address and data
information needed to execute the command. The contents of the register serve
as inputs to the internal state machine. The state machine outputs dictate the
function of the device. Table 1 lists the device bus operations, the inputs and con-
trol 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#
OE#
WE#
A20–0
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
L
L
L
L
H
H
L
I/O
I/O
H
H
H
H
H
L
X
X
L
L
L
L
H
H
X
X
I/O
Synchronous Write
L
L
I/O
Standby (CE#)
H
X
X
X
HIGH Z
HIGH Z
X
X
X
X
Hardware Reset
Burst Read Operations
Load Starting Burst Address
L
L
X
L
H
H
Addr In
HIGH Z
X
H
H
Advance Burst to next address with
appropriate Data presented on the Data Bus
Burst
Data Out
H
Terminate current Burst read cycle
H
X
X
X
H
H
HIGH Z
HIGH Z
HIGH Z
HIGH Z
H
L
X
X
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.
Enhanced VersatileIO™ (VIO) Control
The Enhanced VersatileIO (VIO) control allows the host system to set the voltage
levels that the device generates at its data outputs and the voltages tolerated at
its data and address inputs to the same voltage level that is asserted on the VIO
pin. The device is available with either 1.65–1.95 or 2.7–3.15 VIO. This allows the
device to operate in 1.8 V or 3 V system environments as required.
For example, a VIO of 2.7 – 3.15 volts allows for I/O at the 3 volt level, driving
and receiving signals to and from other 3 V devices on the same bus.
Requirements for Asynchronous Read
Operation (Non-Burst)
To read data from the memory array, the system must first assert a valid address
on A20–A0, while driving AVD# and CE# to VIL. WE# should remain at VIH. The
rising edge of AVD# latches the address. The data will appear on DQ15–DQ0.
12
Am29BDS320G
27243B1 October 1, 2003
SPANSION [ SPANSION ]
