MEM4X16E43VTW-5 Datasheet, PDF (4/24 Pages) List of Unclassifed Manufacturers – 4 MEG x 16 EDO DRAM

DRAM ACCESS (continued)
the upper byte (DQ8-DQ15). General byte and word
access timing is shown in Figures 1 and 2.
A logic HIGH on WE# dictates read mode, while a
logic LOW on WE# dictates write mode. During a
WRITE cycle, data-in (D) is latched by the falling edge
of WE or CAS# (CASL# or CASH#), whichever occurs
last. An EARLY WRITE occurs when WE is taken LOW
prior to either CAS# falling. A LATE WRITE or READ-
MODIFY-WRITE occurs when WE falls after CAS# (CASL#
or CASH#) is taken LOW. During EARLY WRITE cycles,
the data outputs (Q) will remain High-Z, regardless of
the state of OE#. During LATE WRITE or READ-MODIFY-
WRITE cycles, OE# must be taken HIGH to disable the
data outputs prior to applying input data. If a LATE
WRITE or READ-MODIFY-WRITE is attempted while
keeping OE# LOW, no write will occur, and the data
outputs will drive read data from the accessed location.
Additionally, both bytes must always be of the same
mode of operation if both bytes are active. A CAS#
precharge must be satisfied prior to changing modes of
operation between the upper and lower bytes. For
example, an EARLY WRITE on one byte and a LATE
4 MEG x 16
EDO DRAM
WRITE on the other byte are not allowed during the
same cycle. However, an EARLY WRITE on one byte and
a LATE WRITE on the other byte, after a CAS# precharge
has been satisfied, are permissible.
EDO PAGE MODE
DRAM READ cycles have traditionally turned the
output buffers off (High-Z) with the rising edge of
CAS#. If CAS# went HIGH and OE# was LOW (active),
the output buffers would be disabled. The 64Mb EDO
DRAM offers an accelerated page mode cycle by elimi-
nating output disable from CAS# HIGH. This option is
called EDO, and it allows CAS# precharge time (^tCP) to
occur without the output data going invalid (see READ
and EDO-PAGE-MODE READ waveforms).
EDO operates like any DRAM READ or FAST-PAGE-
MODE READ, except data is held valid after CAS# goes
HIGH, as long as RAS# and OE# are held LOW and WE#
is held HIGH. OE# can be brought LOW or HIGH while
CAS# and RAS# are LOW, and the DQs will transition
between valid data and High-Z. Using OE#, there are
RAS#
WORD READ
LOWER BYTE READ
CASL#
CASH#
WE#
LOWER BYTE
(DQ0-DQ7)
OF WORD
UPPER BYTE
(DQ8-DQ15)
OF WORD
STORED
DATA
1
1
0
1
1
1
1
1
OUTPUT
DATA
1
1
0
1
1
1
1
1
OUTPUT
DATA
1
1
0
1
1
1
1
1
STORED
DATA
1
1
0
1
1
1
1
1
STORED
DATA
1
1
0
1
1
1
1
1
0
Z
1
Z
0
Z
1
Z
0
Z
0
Z
0
Z
0
Z
0
0
0
1
1
1
0
0
0
1
1
1
0
0
0
0
0
0
0
0
0
0
0
0
OUTPUT
DATA
1
1
0
1
1
1
1
1
OUTPUT
DATA
1
1
0
1
1
1
1
1
STORED
DATA
1
1
0
1
1
1
1
1
Z
Z
0
Z
Z
1
Z
Z
0
Z
Z
1
Z
Z
0
Z
Z
0
Z
Z
0
Z
Z
0
Z = High-Z
ADDRESS 0
ADDRESS 1
Figure 2
WORD and BYTE READ Example
4