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72V235L10PFG Datasheet(PDF) 6 Page - Integrated Device Technology |
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72V235L10PFG Datasheet(HTML) 6 Page - Integrated Device Technology |
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6 / 25 page  6 IDT72V205/72V215/72V225/72V235/72V245 3.3V CMOS SyncFIFOTM 256 x 18, 512 x 18, 1,024 x 18, 2,048 x 18 and 4,096 x 18 COMMERCIALANDINDUSTRIAL TEMPERATURERANGES MARCH 2013 FUNCTIONALDESCRIPTION TIMING MODES: IDT STANDARD vs FIRST WORD FALL THROUGH (FWFT) MODE The IDT72V205/72V215/72V225/72V235/72V245 support two different timing modes of operation. The selection of which mode will operate is determinedduringconfigurationatReset(RS).Duringa RSoperation,theFirst Load(FL),ReadExpansionInput(RXI),andWriteExpansionInput(WXI)pins areusedtoselectthetimingmodeperthetruthtableshowninTable3.InIDT StandardMode,thefirstwordwrittentoanemptyFIFOwillnotappearonthe dataoutputlinesunlessaspecificreadoperationisperformed.Areadoperation, which consists of activating Read Enable (REN) and enabling a rising Read Clock(RCLK)edge,willshiftthewordfrominternalmemorytothedataoutput lines.InFWFTmode,thefirstwordwrittentoanemptyFIFOisclockeddirectly tothedataoutputlinesafter threetransitionsoftheRCLKsignal.ARENdoes not have to be asserted for accessing the first word. Varioussignals,bothinputandoutputsignalsoperatedifferentlydepending onwhichtimingmodeisineffect. IDT STANDARD MODE In this mode, the status flags, FF, PAF, HF, PAE, and EF operate in the 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 the129th(72V205), 257th(72V215),513th(72V225),1,025th(72V235),and 2,049th(72V245)wordrespectivelywaswrittenintotheFIFO. Continuingto writedataintotheFIFOwillcausetheProgrammableAlmost-FullFlag(PAF) togoLOW.Again,ifnoreadsareperformed, thePAFwillgoLOWafter(256-m) writesfortheIDT72V205,(512-m)writesfortheIDT72V215,(1,024-m)writes fortheIDT72V225,(2,048-m)writesfortheIDT72V235and(4,096–m)writes fortheIDT72V245. Theoffset“m”isthefulloffsetvalue. Thisparameterisalso userprogrammable.SeesectiononProgrammableFlagOffsetLoading. Ifthere isnofulloffsetspecified,thePAFwillbeLOWwhenthedeviceis31awayfrom completelyfullforIDT72V205,63awayfromcompletelyfullforIDT72V215,and 127 away from completely full for the IDT72V225/72V235/72V245. WhentheFIFOisfull,theFullFlag(FF)willgoLOW,inhibitingfurtherwrite operations. Ifnoreadsareperformedafterareset,FFwillgoLOWafterDwrites totheFIFO. D=256writesfortheIDT72V205,512fortheIDT72V215,1,024 for the IDT72V225, 2,048 for the IDT72V235 and 4,096 for the IDT72V245, respectively. If the FIFO is full, the first read operation will cause FF to go HIGH. SubsequentreadoperationswillcausePAFandtheHalf-FullFlag(HF)togo HIGHattheconditionsdescribedinTable1.Iffurtherreadoperationsoccur, withoutwriteoperations,theProgrammableAlmost-EmptyFlag(PAE)willgo LOW when there are n words in the FIFO, where n is the empty offset value. Ifthereisnoemptyoffsetspecified,thePAEwillbeLOWwhenthedeviceis31 awayfromcompletelyemptyforIDT72V205,63awayfromcompletelyempty forIDT72V215,and127awayfromcompletelyemptyforIDT72V225/72V235/ 72V245. Continuing read operations will cause the FIFO to be empty. When thelastwordhasbeenreadfromtheFIFO,theEFwillgoLOWinhibitingfurther read operations. REN is ignored when the FIFO is empty. FIRST WORD FALL THROUGH MODE (FWFT) In this mode, the status flags, IR, PAF, HF, PAE, and OR operate in the manneroutlinedinTable2.TowritedataintototheFIFO,WENmustbeLOW. DatapresentedtotheDATAINlineswillbeclockedintotheFIFOonsubsequent transitionsofWCLK.Afterthefirstwriteisperformed,theOutputReady(OR) flagwillgoLOW.SubsequentwriteswillcontinuetofilluptheFIFO.PAEwillgo HIGHaftern + 2wordshavebeenloadedintotheFIFO,wherenistheempty offsetvalue.ThedefaultsettingforthisvalueisstatedinthefootnoteofTable2. Thisparameterisalsouserprogrammable.SeesectiononProgrammableFlag OffsetLoading. If one continued to write data into the FIFO, and we assumed no read operations were taking place, the HF would toggle to LOW once the 130th (72V205), 258th (72V215), 514th (72V225), 1,026th (72V235), and 2,050th (72V245)wordrespectivelywaswrittenintotheFIFO. Continuingtowritedata intotheFIFOwillcausethePAFtogoLOW.Again,ifnoreadsareperformed, the PAF will go LOW after (257-m) writes for the IDT72V205, (513-m) writes fortheIDT72V215,(1,025-m)writesfortheIDT72V225,(2,049–m)writesfor the IDT72V235 and (4,097–m) writes for the IDT72V245, where m is the full offsetvalue. ThedefaultsettingforthisvalueisstatedinthefootnoteofTable 2. WhentheFIFOisfull,theInputReady(IR)flagwillgoHIGH,inhibitingfurther writeoperations. Ifnoreadsareperformedafterareset,IRwillgoHIGHafter DwritestotheFIFO. D=257writesfortheIDT72V205,513fortheIDT72V215, 1,025 for the IDT72V225, 2,049 for the IDT72V235 and 4,097 for the IDT72V245.NotethattheadditionalwordinFWFTmodeisduetothecapacity ofthememoryplusoutputregister. If the FIFO is full, the first read operation will cause the IR flag to go LOW. Subsequent read operations will cause the PAF and HF to go HIGH at the conditionsdescribedinTable2.Iffurtherreadoperationsoccur,withoutwrite operations,thePAEwillgoLOWwhentherearen+1wordsintheFIFO,where nistheemptyoffsetvalue.Ifthereisnoemptyoffsetspecified,thePAEwillbe LOW when the device is 32 away from completely empty for IDT72V205, 64 away from completely empty for IDT72V215, and 128 away from completely emptyforIDT72V225/72V235/72V245.Continuingreadoperationswillcause the FIFO to be empty. When the last word has been read from the FIFO, OR willgoHIGHinhibitingfurtherreadoperations.RENisignoredwhentheFIFO isempty. PROGRAMMABLEFLAGLOADING FullandEmptyflagoffsetvaluescanbeuserprogrammable.TheIDT72V205/ 72V215/72V225/72V235/72V245 has internal registers for these offsets. DefaultsettingsarestatedinthefootnotesofTable1andTable2.Offsetvalues are loaded into the FIFO using the data input lines D0-D11. To load the offset registers,theLoad(LD)pinandWENpinmustbeheldLOW.Datapresenton D0-D11willbetransferredintotheEmptyOffsetregisteronthefirstLOW-to-HIGH transitionofWCLK.BycontinuingtoholdtheLDandWENpinlow, datapresent onD0-D11willbetransferredintotheFullOffsetregisteronthenexttransition oftheWCLK.ThethirdtransitionagainwritestotheEmptyOffsetregister. Writing alloffsetregistersdoesnothavetooccuratonetime.Oneortwooffsetregisters can be written and then by bringing the LD pin HIGH, the FIFO is returned to normal read/write operation. When the LD pin and WEN are again set LOW, thenextoffsetregisterinsequenceiswritten. |
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