sameꢀbank.TheꢀPRECHARGEꢀcommandꢀshouldꢀbeꢀissuedꢀ
IS42S16400F
IC42S16400F
READS
READ COMMAND
READꢀ burstsꢀ areꢀ initiatedꢀ withꢀ aꢀ READꢀ command,ꢀ asꢀ
shownꢀinꢀtheꢀREADꢀCOMMANDꢀdiagram.
CLK
Theꢀstartingꢀcolumnꢀandꢀbankꢀaddressesꢀareꢀprovidedꢀwithꢀ
theꢀREADꢀcommand,ꢀandꢀautoꢀprechargeꢀisꢀeitherꢀenabledꢀorꢀ
disabled for that burst access. If auto precharge is enabled,
the row being accessed is precharged at the completion of
theꢀburst.ꢀForꢀtheꢀgenericꢀREADꢀcommandsꢀusedꢀinꢀtheꢀfol-
lowing illustrations, auto precharge is disabled.
HIGH-Z
CKE
CS
RAS
DuringꢀREADꢀbursts,ꢀtheꢀvalidꢀdata-outꢀelementꢀfromꢀtheꢀ
starting column address will be available following the
CASꢀlatencyꢀafterꢀtheꢀREADꢀcommand.ꢀEachꢀsubsequentꢀ
data-outꢀelementꢀwillꢀbeꢀvalidꢀbyꢀtheꢀnextꢀpositiveꢀclockꢀ
edge.ꢀTheꢀCASꢀLatencyꢀdiagramꢀshowsꢀgeneralꢀtiming
for each possible CAS latency setting.
CAS
WE
COLUMN ADDRESS
AUTO PRECHARGE
Uponꢀcompletionꢀofꢀaꢀburst,ꢀassumingꢀnoꢀotherꢀcommandsꢀ
haveꢀbeenꢀinitiated,ꢀtheꢀDQsꢀwillꢀgoꢀHigh-Z.ꢀAꢀfull-pageꢀburstꢀ
will continue until terminated. (At the end of the page, it will
wrap to column 0 and continue.)
A0-A7
A8, A9, A11
A10
DataꢀfromꢀanyꢀREADꢀburstꢀmayꢀbeꢀtruncatedꢀwithꢀaꢀsub-
sequentꢀREADꢀcommand,ꢀandꢀdataꢀfromꢀaꢀfixed-lengthꢀ
READꢀburstꢀmayꢀbeꢀimmediatelyꢀfollowedꢀbyꢀdataꢀfromꢀaꢀ
READꢀcommand.ꢀInꢀeitherꢀcase,ꢀaꢀcontinuousꢀflowꢀofꢀdataꢀ
canꢀbeꢀmaintained.ꢀTheꢀfirstꢀdataꢀelementꢀfromꢀtheꢀnewꢀ
burst follows either the last element of a completed burst
or the last desired data element of a longer burst which
is being truncated.
NO PRECHARGE
BANK ADDRESS
BA0, BA1
TheꢀDQMꢀinputꢀisꢀusedꢀtoꢀavoidꢀI/Oꢀcontention,ꢀasꢀshownꢀ
inꢀFiguresꢀRW1ꢀandꢀRW2.ꢀTheꢀDQMꢀsignalꢀmustꢀbeꢀas-
sertedꢀ(HIGH)ꢀatꢀleastꢀthreeꢀclocksꢀpriorꢀtoꢀtheꢀWRITEꢀ
commandꢀ(DQMꢀlatencyꢀisꢀtwoꢀclocksꢀforꢀoutputꢀbuffers)ꢀ
toꢀsuppressꢀdata-outꢀfromꢀtheꢀREAD.ꢀOnceꢀtheꢀWRITEꢀ
commandꢀisꢀregistered,ꢀtheꢀDQsꢀwillꢀgoꢀHigh-Zꢀ(orꢀremainꢀ
High-Z),ꢀregardlessꢀofꢀtheꢀstateꢀofꢀtheꢀDQMꢀsignal,ꢀprovidedꢀ
theꢀDQMꢀwasꢀactiveꢀonꢀtheꢀclockꢀjustꢀpriorꢀtoꢀtheꢀWRITEꢀ
commandꢀthatꢀtruncatedꢀtheꢀREADꢀcommand.ꢀIfꢀnot,ꢀtheꢀ
secondꢀWRITEꢀwillꢀbeꢀanꢀinvalidꢀWRITE.ꢀForꢀexample,ꢀifꢀ
DQMꢀwasꢀLOWꢀduringꢀT4ꢀinꢀFigureꢀRW2,ꢀthenꢀtheꢀWRITEsꢀ
atꢀT5ꢀandꢀT7ꢀwouldꢀbeꢀvalid,ꢀwhileꢀtheꢀWRITEꢀatꢀT6ꢀwouldꢀ
be invalid.
TheꢀnewꢀREADꢀcommandꢀshouldꢀbeꢀissuedꢀxcyclesbefore
the clock edge at which the last desired data element is
valid, where x equalsꢀtheꢀCASꢀlatencyꢀminusꢀone.ꢀThisꢀisꢀ
shownꢀinꢀConsecutiveꢀREADꢀBurstsꢀforꢀCASꢀlatenciesꢀofꢀ
twoꢀandꢀthree;ꢀdataꢀelementꢀn +ꢀ3ꢀisꢀeitherꢀtheꢀlastꢀofꢀaꢀ
burstꢀofꢀfourꢀorꢀtheꢀlastꢀdesiredꢀofꢀaꢀlongerꢀburst.ꢀTheꢀ64Mbꢀ
SDRAMꢀusesꢀaꢀpipelinedꢀarchitectureꢀandꢀthereforeꢀdoesꢀ
not require the 2n rule associated with a prefetch architec-
ture.ꢀAꢀREADꢀcommandꢀcanꢀbeꢀinitiatedꢀonꢀanyꢀclockꢀcycleꢀ
followingꢀaꢀpreviousꢀREADꢀcommand.ꢀFull-speedꢀrandomꢀ
read accesses can be performed to the same bank, as
shownꢀinꢀRandomꢀREADꢀAccesses,ꢀorꢀeachꢀsubsequentꢀ
READꢀmayꢀbeꢀperformedꢀtoꢀaꢀdifferentꢀbank.
TheꢀDQMꢀsignalꢀmustꢀbeꢀde-assertedꢀpriorꢀtoꢀtheꢀWRITEꢀ
commandꢀ(DQMꢀlatencyꢀisꢀzeroꢀclocksꢀforꢀinputꢀbuffers)ꢀ
to ensure that the written data is not masked.
DataꢀfromꢀanyꢀREADꢀburstꢀmayꢀbeꢀtruncatedꢀwithꢀaꢀsub-
sequentꢀWRITEꢀcommand,ꢀandꢀdataꢀfromꢀaꢀfixed-lengthꢀ
READꢀburstꢀmayꢀbeꢀimmediatelyꢀfollowedꢀbyꢀdataꢀfromꢀaꢀ
WRITEꢀcommandꢀ(subjectꢀtoꢀbusꢀturnaroundꢀlimitations).ꢀ
TheꢀWRITEꢀburstꢀmayꢀbeꢀinitiatedꢀonꢀtheꢀclockꢀedgeꢀim-
mediately following the last (or last desired) data element
fromꢀtheꢀREADꢀburst,ꢀprovidedꢀthatꢀI/Oꢀcontentionꢀcanꢀbeꢀ
avoided. In a given system design, there may be a pos-
sibilityꢀthatꢀtheꢀdeviceꢀdrivingꢀtheꢀinputꢀdataꢀwillꢀgoꢀLow-Zꢀ
beforeꢀtheꢀSDRAMꢀDQsꢀgoꢀHigh-Z.ꢀInꢀthisꢀcase,ꢀatꢀleastꢀ
a single-cycle delay should occur between the last read
dataꢀandꢀtheꢀWRITEꢀcommand.
Aꢀfixed-lengthꢀREADꢀburstꢀmayꢀbeꢀfollowedꢀby,ꢀorꢀtruncatedꢀ
with, aPRECHARGE commandtothesamebank(provided
that auto precharge was not activated), and a full-page burst
mayꢀbeꢀtruncatedꢀwithꢀaꢀPRECHARGEꢀcommandꢀtoꢀtheꢀ
x cycles before the clock edge at which the last desired
data element is valid, where x equals the CAS latency
minusꢀone.ꢀThisꢀisꢀshownꢀinꢀtheꢀREADꢀtoꢀPRECHARGEꢀ
20
Integrated Silicon Solution, Inc. — www.issi.com
Rev. A
03/19/08
ISSI [ INTEGRATED SILICON SOLUTION, INC ]
