precharge.TheꢀdisadvantageꢀofꢀtheꢀPRECHARGEcommand
IS42S16400F
IC42S16400F
AnꢀexampleꢀisꢀshownꢀinꢀWRITEꢀtoꢀWRITEꢀdiagram.ꢀDataꢀ
n +ꢀ1ꢀisꢀeitherꢀtheꢀlastꢀofꢀaꢀburstꢀofꢀtwoꢀorꢀtheꢀlastꢀdesiredꢀ
ofꢀaꢀlongerꢀburst.ꢀTheꢀ64MbꢀSDRAMꢀ usesꢀ aꢀ pipelinedꢀ
architecture and therefore does not require the 2n rule as-
sociatedꢀwithꢀaꢀprefetchꢀarchitecture.ꢀAꢀWRITEꢀcommandꢀ
can be initiated on any clock cycle following a previous
WRITEꢀcommand.ꢀFull-speedꢀrandomꢀwriteꢀaccessesꢀwithinꢀ
a page can be performed to the same bank, as shown in
RandomꢀWRITEꢀCycles,ꢀorꢀeachꢀsubsequentꢀWRITEꢀmayꢀ
be performed to a different bank.
WRITEs
WRITEꢀburstsꢀareꢀinitiatedꢀwithꢀaꢀWRITEꢀcommand,ꢀasꢀ
shownꢀinꢀWRITEꢀCommandꢀdiagram.
WRITE Command
CLK
HIGH - Z
CKE
DataꢀforꢀanyꢀWRITEꢀburstꢀmayꢀbeꢀtruncatedꢀwithꢀaꢀsubse-
quentꢀREADꢀcommand,ꢀandꢀdataꢀforꢀaꢀfixed-lengthꢀWRITEꢀ
burstꢀmayꢀbeꢀimmediatelyꢀfollowedꢀbyꢀaꢀsubsequentꢀREADꢀ
command.ꢀOnceꢀtheꢀREADꢀcommandꢀisꢀregistered,ꢀtheꢀ
dataꢀinputsꢀwillꢀbeꢀignored,ꢀandꢀWRITEsꢀwillꢀnotꢀbeꢀex-
ecuted.ꢀAnꢀexampleꢀisꢀshownꢀinꢀWRITEꢀtoꢀREAD.ꢀDataꢀn
+ꢀ1ꢀisꢀeitherꢀtheꢀlastꢀofꢀaꢀburstꢀofꢀtwoꢀorꢀtheꢀlastꢀdesiredꢀ
of a longer burst.
CS
RAS
CAS
WE
Dataꢀ forꢀ aꢀ fixed-lengthꢀ WRITEꢀ burstꢀ mayꢀ beꢀ followedꢀ
by,ꢀorꢀtruncatedꢀwith,ꢀaꢀPRECHARGEꢀcommandꢀtoꢀtheꢀ
same bank (provided that auto precharge was not acti-
vated),ꢀandꢀaꢀfull-pageꢀWRITEꢀburstꢀmayꢀbeꢀtruncatedꢀ
withꢀaꢀPRECHARGEꢀcommandꢀtoꢀtheꢀsameꢀbank.ꢀTheꢀ
PRECHARGEꢀcommandꢀshouldꢀbeꢀissuedꢀtw r after the
clock edge at which the last desired input data element
isꢀregistered.ꢀTheꢀautoꢀprechargeꢀmodeꢀrequiresꢀaꢀtw r of
at least one clock plus time, regardless of frequency. In
addition,ꢀwhenꢀtruncatingꢀaꢀWRITEꢀburst,ꢀtheꢀDQMꢀsignalꢀ
must be used to mask input data for the clock edge prior
to,ꢀandꢀtheꢀclockꢀedgeꢀcoincidentꢀwith,ꢀtheꢀPRECHARGEꢀ
command.ꢀAnꢀexampleꢀisꢀshownꢀinꢀtheꢀWRITEꢀtoꢀPRE-
CHARGEꢀdiagram.ꢀDataꢀn+1ꢀisꢀeitherꢀtheꢀlastꢀofꢀaꢀburstꢀ
ofꢀtwoꢀorꢀtheꢀlastꢀdesiredꢀofꢀaꢀlongerꢀburst.ꢀFollowingꢀtheꢀ
PRECHARGEꢀcommand,ꢀaꢀsubsequentꢀcommandꢀtoꢀtheꢀ
same bank cannot be issued until tr p is met.
COLUMN ADDRESS
AUTO PRECHARGE
A0-A7
A8, A9, A11
A10
NO PRECHARGE
BANK ADDRESS
BA0, BA1
Theꢀstartingꢀcolumnꢀandꢀbankꢀaddressesꢀareꢀprovidedꢀwithꢀ
theꢀWRITEꢀcommand,ꢀandꢀautoꢀprechargeꢀisꢀeitherꢀenabledꢀ
or disabled for that access. If auto precharge is enabled,
the row being accessed is precharged at the completion of
theꢀburst.ꢀForꢀtheꢀgenericꢀWRITEꢀcommandsꢀusedꢀinꢀtheꢀ
following illustrations, auto precharge is disabled.
Inꢀtheꢀcaseꢀofꢀaꢀfixed-lengthꢀburstꢀbeingꢀexecutedꢀtoꢀcomple-
tion,ꢀaꢀPRECHARGEꢀcommandꢀissuedꢀatꢀtheꢀoptimumꢀ
time (as described above) provides the same operation that
wouldꢀresultꢀfromꢀtheꢀsameꢀfixed-lengthꢀburstꢀwithꢀautoꢀ
DuringꢀWRITEꢀbursts,ꢀtheꢀfirstꢀvalidꢀdata-in element will be
registeredcoincidentwiththeWRITEꢀcommand.Subsequent
data elements will be registered on each successive posi-
tiveꢀclockꢀedge.ꢀUponꢀcompletionꢀofꢀaꢀfixed-lengthꢀburst,ꢀ
assuming no other commands have been initiated, the
DQsꢀwillꢀremainꢀHigh-Zꢀandꢀanyꢀadditionalꢀinputꢀdataꢀwillꢀ
beꢀignoredꢀ(seeꢀWRITEꢀBurst).ꢀAꢀfull-pageꢀburstꢀwillꢀcon-
tinue until terminated. (At the end of the page, it will wrap
to column 0 and continue.)
is that it requires that the command and address buses be
availableꢀatꢀtheꢀappropriateꢀtimeꢀtoꢀissueꢀtheꢀcommand;ꢀtheꢀ
advantageꢀofꢀtheꢀPRECHARGEꢀcommandꢀisꢀthatꢀitꢀcanꢀbeꢀ
usedꢀtoꢀtruncateꢀfixed-lengthꢀorꢀfull-pageꢀbursts.
Fixed-lengthꢀorꢀfull-pageꢀWRITEꢀburstsꢀcanꢀbeꢀtruncatedꢀ
withꢀtheꢀBURSTꢀTERMINATEꢀcommand.ꢀWhenꢀtruncat-
ingꢀaꢀWRITEꢀburst,ꢀtheꢀinputꢀdataꢀappliedꢀcoincidentꢀwithꢀ
theꢀBURSTꢀTERMINATEꢀcommandꢀwillꢀbeꢀignored.ꢀTheꢀ
lastꢀdataꢀwrittenꢀ(providedꢀthatꢀDQMꢀisꢀLOWꢀatꢀthatꢀtime)ꢀ
will be the input data applied one clock previous to the
BURSTꢀTERMINATEꢀcommand.ꢀThisꢀisꢀshownꢀinꢀWRITEꢀ
BurstꢀTermination,ꢀwhereꢀdataꢀn is the last desired data
element of a longer burst.
DataꢀforꢀanyꢀWRITEꢀburstꢀmayꢀbeꢀtruncatedꢀwithꢀaꢀsubse-
quentꢀWRITEꢀcommand,ꢀandꢀdataꢀforꢀaꢀfixed-lengthꢀWRITEꢀ
burstꢀmayꢀbeꢀimmediatelyꢀfollowedꢀbyꢀdataꢀforꢀaꢀWRITEꢀ
command.ꢀTheꢀnewꢀWRITEꢀcommandꢀcanꢀbeꢀissuedꢀonꢀ
anyꢀclockꢀfollowingꢀtheꢀpreviousꢀWRITEꢀcommand,ꢀandꢀtheꢀ
data provided coincident with the new command applies to
the new command.
Integrated Silicon Solution, Inc. — www.issi.comꢀ
27
Rev. A
03/19/08
ISSI [ INTEGRATED SILICON SOLUTION, INC ]
