IDT72T7285/72T7295/72T72105/72T72115 2.5V TeraSync
16,384 x 72, 32,768 x 72, 65,536 x 72, 131,072 x 72
72-BIT FIFO
COMMERCIAL AND INDUSTRIAL
TEMPERATURE RANGES
value.ThedefaultsettingforthisvalueisstatedinthefootnoteofTable3.
In FWFT mode, the PAF will go LOW after (16,385-m) writes for the
IDT72T7285,(32,769-m)writesfortheIDT72T7295,(65,537-m)writesforthe
IDT72T72105and(131,073-m)writes forthe IDT72T72115, where mis the
fulloffsetvalue.Thedefaultsettingforthisvalueisstatedin Table4.
SeeFigure23,SynchronousProgrammableAlmost-FullFlagTiming(IDT
StandardandFWFTMode),fortherelevanttiminginformation.
IfasynchronousPAFconfigurationisselected,thePAFisassertedLOW
ontheLOW-to-HIGHtransitionoftheWriteClock(WCLK). PAFisresettoHIGH
ontheLOW-to-HIGHtransitionoftheReadClock(RCLK). IfsynchronousPAF
configurationisselected,thePAFisupdatedontherisingedgeofWCLK. See
Figure25,AsynchronousAlmost-FullFlagTiming(IDTStandardandFWFT
Mode).
OUTPUTS:
FULL FLAG ( FF/IR )
Thisisadualpurposepin. InIDTStandardmode,theFullFlag (FF) function
is selected. When the FIFO is full, FF will go LOW, inhibiting further write
operations. WhenFF isHIGH,theFIFOisnotfull. Ifnoreadsareperformed
after a reset (either MRS orPRS), FF willgoLOWafterDwrites tothe FIFO
(D =16,384forthe IDT72T7285, 32,768forthe IDT72T7295, 65,536forthe
IDT72T72105and131,072fortheIDT72T72115).SeeFigure11,WriteCycle
andFullFlagTiming(IDTStandardMode),fortherelevanttiminginformation.
InFWFTmode, the InputReady(IR)functionis selected. IRgoes LOW
whenmemoryspaceis availableforwritingindata. Whenthereis nolonger
anyfreespaceleft,IRgoesHIGH,inhibitingfurtherwriteoperations. Ifnoreads
areperformedafterareset(eitherMRSorPRS),IRwillgoHIGHafterD writes
to the FIFO (D =16,385 for the IDT72T7285, 32,769 for the IDT72T7295,
65,537fortheIDT72T72105and131,073fortheIDT72T72115).SeeFigure
14, WriteTiming(FWFTMode),fortherelevanttiminginformation.
TheIRstatusnotonlymeasuresthecontentsoftheFIFOmemory,butalso
countsthepresenceofawordintheoutputregister. Thus,inFWFTmode,the
totalnumberofwritesnecessarytodeassertIRisonegreaterthanneededto
assert FF in IDT Standard mode.
Note,whenthedeviceisinRetransmitmode,thisflagisacomparisonofthe
writepointertothe‘marked’location.Thisdiffersfromnormalmodewherethis
flagis acomparisonofthewritepointertothereadpointer.
PROGRAMMABLEALMOST-EMPTYFLAG(PAE)
TheProgrammableAlmost-Emptyflag(PAE)willgoLOWwhentheFIFO
reachesthealmost-emptycondition.InIDTStandardmode,PAEwillgoLOW
whenthere are nwords orless inthe FIFO. The offset“n”is the emptyoffset
value.ThedefaultsettingforthisvalueisstatedinthefootnoteofTable 1.
In FWFT mode, the PAE will go LOW when there are n+1 words or less
intheFIFO.Thedefaultsettingforthis valueis statedinTable2.
See Figure 24, Synchronous ProgrammableAlmost-EmptyFlagTiming
(IDTStandardandFWFTMode), forthe relevanttiminginformation.
IfasynchronousPAEconfigurationisselected,thePAEisassertedLOW
ontheLOW-to-HIGHtransitionoftheReadClock(RCLK). PAEisresettoHIGH
ontheLOW-to-HIGHtransitionoftheWriteClock(WCLK). IfsynchronousPAE
configurationisselected,thePAEisupdatedontherisingedgeofRCLK. See
Figure 26, Asynchronous Programmable Almost-Empty Flag Timing (IDT
Standard and FWFT Mode).
FF/IRissynchronousandupdatedontherisingedgeofWCLK.FF/IRare
doubleregister-bufferedoutputs.
Note,whenthedeviceisinRetransmitmode,thisflagisacomparisonofthe
writepointertothe‘marked’location.Thisdiffersfromnormalmodewherethis
flagis acomparisonofthewritepointertothereadpointer.
EMPTY FLAG ( EF/OR )
Thisisadualpurposepin. IntheIDTStandardmode,theEmptyFlag(EF)
functionisselected. WhentheFIFOisempty,EFwillgoLOW,inhibitingfurther
readoperations. WhenEFisHIGH,theFIFOisnotempty.SeeFigure12,Read
Cycle, EmptyFlagandFirstWordLatencyTiming(IDTStandardMode),for
therelevanttiminginformation.
InFWFTmode,theOutputReady(OR)functionisselected.ORgoesLOW
atthesametimethatthefirstwordwrittentoanemptyFIFOappearsvalidon
theoutputs. ORstaysLOWaftertheRCLKLOWtoHIGHtransitionthatshifts
thelastwordfromtheFIFOmemorytotheoutputs. OR goesHIGHonlywith
atrueread(RCLKwithREN=LOW). Thepreviousdatastaysattheoutputs,
indicatingthelastwordwasread. FurtherdatareadsareinhibiteduntilORgoes
LOWagain.SeeFigure15,ReadTiming(FWFTMode),fortherelevanttiming
information.
HALF-FULL FLAG ( HF )
Thisoutputindicatesahalf-fullFIFO.TherisingWCLKedgethatfillstheFIFO
beyondhalf-fullsetsHFLOW.TheflagremainsLOWuntilthedifferencebetween
thewriteandreadpointersbecomeslessthanorequaltohalfofthetotaldepth
ofthedevice;therisingRCLKedgethataccomplishesthisconditionsetsHF
HIGH.
InIDTStandardmode,ifnoreadsareperformedafterreset(MRSorPRS),
HF will go LOW after (D/2 + 1) writes to the FIFO, where D = 16,384 for the
IDT72T7285, 32,768fortheIDT72T7295, 65,536fortheIDT72T72105and
131,072 for the IDT72T72115.
In FWFT mode, if no reads are performed after reset (MRS or PRS), HF
will go LOW after (D-1/2 + 2) writes to the FIFO, where D = 16,385 for the
IDT72T7285, 32,769fortheIDT72T7295, 65,537fortheIDT72T72105and
131,073 for the IDT72T72115.
See Figure 27, Half-Full Flag Timing (IDT Standard and FWFT Modes),
fortherelevanttiminginformation.BecauseHFisupdatedbybothRCLKand
WCLK,itisconsideredasynchronous.
EF/OR is synchronous and updated on the rising edge of RCLK.
InIDTStandardmode, EFis a double register-bufferedoutput. InFWFT
mode,ORisatripleregister-bufferedoutput.
PROGRAMMABLE ALMOST-FULL FLAG (PAF )
The Programmable Almost-Full flag (PAF) will go LOW when the FIFO
reaches the almost-full condition. In IDT Standard mode, if no reads are
performedafterreset(MRS),PAFwillgoLOWafter(D - m)wordsarewritten
totheFIFO.ThePAFwillgoLOWafter(16,384-m)writesfortheIDT72T7285,
(32,768-m)writesfortheIDT72T7295,(65,536-m)writesfortheIDT72T72105
and(131,072-m)writes fortheIDT72T72115.Theoffset“m”is thefulloffset
24
IDT [ INTEGRATED DEVICE TECHNOLOGY ]
