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 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 ma-
chine. The state machine outputs dictate the function 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. Device Bus Operations
Operation
CE#
L
OE#
L
WE# A16–21 A/DQ0–15 RESET# CLK
AVD#
Asynchronous Read
Write
H
L
Addr In
I/O
H
H
H
L
H/L
H/L
H/L
X
L
H
Addr In
I/O
Standby (CE#)
H
X
X
X
X
X
HIGH Z
HIGH Z
X
X
Hardware Reset
Burst Read Operations
Load Starting Burst Address
X
X
L
L
H
L
H
H
Addr In
X
Addr In
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
X
X
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
H
H
X
I/O
H
Legend: L = Logic 0, H = Logic 1, X = Don’t Care.
ensures that no spurious alteration 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
assert a valid address on A/DQ0–A/DQ15 and
Requirements for Synchronous (Burst)
Read Operation
A16–A21, while AVD# and CE# are at V . WE#
IL
The device is capable of four different burst read modes
(see Table 8): continuous burst read; and 8-, 16-, and
32-word linear burst reads with wrap around capability.
should remain at V . Note that CLK must not be
switching during asynchronous read operations. The
rising edge of AVD# latches the address, after which
IH
the system can drive OE# to V . The data will appear
IL
Continuous Burst
on A/DQ0–A/DQ15. (See Figure 11.) Since the mem-
ory array is divided into four banks, each bank remains
enabled for read access until the command register
contents are altered.
When the device first powers up, it is enabled for asyn-
chronous read operation. The device will automatically
be enabled for burst mode on the first rising edge on
the CLK input, while AVD# is held low for one clock
cycle. Prior to activating the clock signal, the system
should determine how many wait states are desired for
Address access time (t
) is equal to the delay from
ACC
stable addresses to valid output data. The chip enable
access time (t ) is the delay from the stable
the initial word (t
) of each burst session. The
CE
IACC
addresses and stable CE# to valid data at the outputs.
system would then write the Set Configuration Register
command sequence. The system may optionally acti-
vate the PS mode (see “Power Saving Function”) by
writing the Enable PS Mode command sequence at
this time, but note that the PS mode can only be dis-
abled by a hardware reset. (See “Command Defini-
The output enable access time (t ) is the delay from
OE
the falling edge of OE# to valid data at the output.
The internal state machine is set for reading array data
upon device power-up, or after a hardware reset. This
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