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IDT72V275 Datasheet(PDF) 7 Page - Integrated Device Technology |
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IDT72V275 Datasheet(HTML) 7 Page - Integrated Device Technology |
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7 / 25 page  7 COMMERCIAL AND INDUSTRIAL TEMPERATURE RANGES IDT72V275/72V285 3.3V CMOS SUPERSYNC FIFOTM 32,768 x 18 and 65,536 x 18 WhenconfiguredinIDTStandardmode,theEFandFFoutputsaredouble register-bufferedoutputs. Relevant timing diagrams for IDT Standard mode can be found in Figure 7, 8 and 11. FIRST WORD FALL THROUGH MODE (FWFT) Inthismode,thestatusflags,IR,PAF,HF,PAE,andORoperateinthe manneroutlinedinTable2.TowritedataintototheFIFO,WENmustbeLOW. DatapresentedtotheDATAINlineswillbeclockedintotheFIFOonsubsequent transitionsofWCLK.Afterthefirstwriteisperformed,theOutputReady(OR) flagwillgoLOW.SubsequentwriteswillcontinuetofilluptheFIFO.PAEwill goHIGHaftern + 2wordshavebeenloadedintotheFIFO,wherenistheempty offsetvalue.ThedefaultsettingforthisvalueisstatedinthefootnoteofTable2. Thisparameterisalsouserprogrammable.SeesectiononProgrammableFlag OffsetLoading. If one continued to write data into the FIFO, and we assumed no read operationsweretakingplace,theHFwouldtoggletoLOWoncethe16,386th wordfortheIDT72V275and 32,770thwordfortheIDT72V285,respectively waswrittenintotheFIFO. ContinuingtowritedataintotheFIFOwillcausethe PAFtogoLOW.Again,ifnoreadsareperformed, thePAFwillgoLOWafter (32,769-m)writesfortheIDT72V275 and(65,537-m)writesfortheIDT72V285, wheremisthefulloffsetvalue. Thedefaultsettingforthisvalueisstatedinthe footnoteofTable2. WhentheFIFOisfull,theInputReady(IR)flagwillgoHIGH,inhibitingfurther writeoperations. Ifnoreadsareperformedafterareset,IRwillgoHIGHafter DwritestotheFIFO. D = 32,769writesfortheIDT72V275and65,537writes fortheIDT72V285,respectively.NotethattheadditionalwordinFWFTmode is due to the capacity of the memory plus output register. If the FIFO is full, the first read operation will cause the IRflagtogoLOW. Subsequent read operations will cause the PAF and HF to go HIGH at the conditionsdescribedinTable2.Iffurtherreadoperationsoccur,withoutwrite operations,thePAEwillgoLOWwhentherearen+1wordsintheFIFO,where nistheemptyoffsetvalue.ContinuingreadoperationswillcausetheFIFOto becomeempty.WhenthelastwordhasbeenreadfromtheFIFO,ORwillgo HIGH inhibiting further read operations. REN is ignored when the FIFO is empty. When configured in FWFT mode, the OR flag output is triple register- buffered,andtheIRflagoutputisdoubleregister-buffered. RelevanttimingdiagramsforFWFTmodecanbefoundinFigure9,10and 12. PROGRAMMING FLAG OFFSETS FullandEmptyFlagoffsetvaluesareuserprogrammable.TheIDT72V275/ 72V285hasinternalregistersfortheseoffsets.Defaultsettingsarestatedinthe footnotesofTable1andTable2.OffsetvaluescanbeprogrammedintotheFIFO inoneoftwoways;serialorparallelloadingmethod.Theselectionoftheloading methodisdoneusingtheLD(Load)pin.DuringMasterReset,thestateofthe LD input determines whether serial or parallel flag offset programming is enabled. A HIGH on LD during Master Reset selects serial loading of offset values and in addition, sets a default PAE offset value of 3FFH (a threshold 1,023wordsfromtheemptyboundary),andadefaultPAFoffsetvalueof3FFH (athreshold1,023wordsfromthefullboundary). ALOWonLDduringMaster Resetselectsparallelloadingofoffsetvalues,andinaddition,setsadefaultPAE offset value of 07FH (a threshold 127 words from the empty boundary), and a default PAF offset value of 07FH (a threshold 127 words from the full boundary). See Figure 3, Offset Register Location and Default Values. InadditiontoloadingoffsetvaluesintotheFIFO,italsopossibletoreadthe currentoffsetvalues.It isonlypossibletoreadoffsetvaluesviaparallelread. FUNCTIONALDESCRIPTION TIMING MODES: IDT STANDARD vs FIRST WORD FALL THROUGH (FWFT) MODE TheIDT72V275/72V285supporttwodifferenttimingmodesofoperation: IDTStandardmodeorFirstWordFallThrough(FWFT)mode. Theselection ofwhichmodewilloperateisdeterminedduringMasterReset,bythestateof the FWFT/SI input. If,atthetimeofMasterReset,FWFT/SIisLOW,thenIDTStandardmode will be selected. This mode uses the Empty Flag (EF) to indicate whether or notthereareanywordspresentintheFIFO.ItalsousestheFullFlagfunction (FF)toindicatewhetherornottheFIFOhasanyfreespaceforwriting. InIDT Standard mode, every word read from the FIFO, including the first, must be requested using the Read Enable (REN) and RCLK. If,atthetimeofMasterReset,FWFT/SIisHIGH,thenFWFTmodewillbe selected. ThismodeusesOutputReady(OR)toindicatewhetherornotthere isvaliddataatthedataoutputs(Qn). ItalsousesInputReady(IR)toindicate whether or not the FIFO has any free space for writing. In the FWFT mode, thefirstwordwrittentoanemptyFIFOgoesdirectlytoQnafterthreeRCLKrising edges,REN=LOWisnotnecessary. Subsequentwordsmustbeaccessed using the Read Enable (REN) and RCLK. Varioussignals,bothinputandoutputsignalsoperatedifferentlydepending onwhichtimingmodeisineffect. IDT STANDARD MODE Inthismode,thestatusflags,FF,PAF,HF,PAE,andEFoperateinthe manneroutlinedinTable1.TowritedataintototheFIFO,WriteEnable(WEN) mustbeLOW.DatapresentedtotheDATAINlineswillbeclockedintotheFIFO on subsequent transitions of the Write Clock (WCLK). After the first write is performed,theEmptyFlag(EF)willgoHIGH.Subsequentwriteswillcontinue tofilluptheFIFO.TheProgrammableAlmost-Emptyflag(PAE)willgoHIGH aftern + 1wordshavebeenloadedintotheFIFO,wherenistheemptyoffset value.ThedefaultsettingforthisvalueisstatedinthefootnoteofTable1.This parameter is also user programmable. See section on Programmable Flag OffsetLoading. If one continued to write data into the FIFO, and we assumed no read operationsweretakingplace,theHalf-Fullflag(HF)wouldtoggletoLOWonce the 16,385th word for IDT72V275 and 32,769th word for IDT72V285 respectivelywaswrittenintotheFIFO. ContinuingtowritedataintotheFIFO willcausetheProgrammableAlmost-Fullflag(PAF)togoLOW.Again,ifno reads are performed, the PAF will go LOW after (32,768-m) writes for the IDT72V275and(65,536-m)writesfortheIDT72V285. Theoffset“m”isthefull offsetvalue.ThedefaultsettingforthisvalueisstatedinthefootnoteofTable1. Thisparameterisalsouserprogrammable.SeesectiononProgrammableFlag OffsetLoading. WhentheFIFOisfull,theFullFlag(FF)willgoLOW,inhibitingfurtherwrite operations. Ifnoreadsareperformedafterareset,FFwillgoLOWafterDwrites to the FIFO. D = 32,768 writes for the IDT72V275 and 65,536 for the IDT72V285,respectively. If the FIFO is full, the first read operation will cause FF to go HIGH. Subsequent read operations will cause PAF and HF to go HIGH at the conditionsdescribedinTable1.Iffurtherreadoperationsoccur,withoutwrite operations, PAE will go LOW when there are n words in the FIFO, where n is the empty offset value. Continuing read operations will cause the FIFO to becomeempty.WhenthelastwordhasbeenreadfromtheFIFO,theEFwill goLOWinhibitingfurtherreadoperations.RENisignoredwhentheFIFOis empty. |
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