128Mb: x4, x8, x16
SDRAM
READs
READ bursts are initiated with a READ command, as
shown in Figure 5.
Upon completion of a burst, assuming no other com-
mands have been initiated, the DQs will go High-Z. A full-
page burst will continue until terminated. (At the end of
the page, it will wrap to column 0 and continue.)
Data from any READ burst may be truncated with a
subsequentREADcommand,anddatafromafixed-length
READ burst may be immediately followed by data from a
READcommand. Ineithercase, acontinuousflowofdata
can be maintained. The first data element from the new
burst follows either the last element of a completed burst
or the last desired data element of a longer burst that is
being truncated. The new READ command should be
issued x cycles before the clock edge at which the last
desired data element is valid, where x equals the CAS
latency minus one.
The starting column and bank addresses are provided
with the READ command, and auto precharge is either
enabledordisabledforthatburstaccess.Ifautoprecharge
is enabled, the row being accessed is precharged at the
completion of the burst. For the generic READ com-
mandsusedinthefollowingillustrations, autoprecharge
is disabled.
During READ bursts, the valid data-out element from
the starting column address will be available following
the CAS latency after the READ command. Each subse-
quent data-out element will be valid by the next positive
clock edge. Figure 6 shows general timing for each pos-
sible CAS latency setting.
T0
T1
T2
T3
CLK
CLK
CKE
CS#
HIGH
COMMAND
READ
NOP
t
NOP
t
LZ
OH
DOUT
DQ
t
AC
CAS Latency = 2
RAS#
CAS#
WE#
T0
T1
T2
T3
T4
CLK
COMMAND
READ
NOP
NOP
NOP
t
t
LZ
OH
A0-A9, A11: x4
A0-A9: x8
COLUMN
ADDRESS
DOUT
DQ
A0-A8: x16
t
AC
A11: x8
CAS Latency = 3
A9, A11: x16
DON’T CARE
UNDEFINED
ENABLE AUTO PRECHARGE
DISABLE AUTO PRECHARGE
A10
Figure 6
CAS Latency
BANK
ADDRESS
BA0,1
Figure 5
READ Command
128Mb: x4, x8, x16 SDRAM
128MSDRAM_E.p65 – Rev. E; Pub. 1/02
Micron Technology, Inc., reserves the right to change products or specifications without notice.
©2001, Micron Technology, Inc.
16
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