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
If the FIFO is full, the first read operation will cause FF to go HIGH.
SubsequentreadoperationswillcausePAFandHFtogoHIGHattheconditions
describedinTable3.Iffurtherreadoperationsoccur,withoutwriteoperations,
PAE will go LOW when there are n words in the FIFO, where n is the empty
offsetvalue.ContinuingreadoperationswillcausetheFIFOtobecomeempty.
WhenthelastwordhasbeenreadfromtheFIFO,theEFwillgoLOWinhibiting
further read operations. REN is ignored when the FIFO is empty.
WhenconfiguredinIDTStandardmode,theEFandFFoutputsaredouble
register-bufferedoutputs.
FUNCTIONALDESCRIPTION
TIMING MODES: IDT STANDARD vs FIRST WORD FALL THROUGH
(FWFT) MODE
The IDT72T7285/72T7295/72T72105/72T72115 support two different
timing modes of operation: IDT Standard mode or First Word Fall Through
(FWFT)mode.Theselectionofwhichmodewilloperateisdeterminedduring
MasterReset,bythestateoftheFWFT/SIinput.
If,atthetimeofMasterReset,FWFT/SIisLOW,thenIDTStandardmode
willbeselected.ThismodeusestheEmptyFlag(EF)toindicatewhetherornot
thereareanywordspresentintheFIFO.ItalsousestheFullFlagfunction(FF)
to indicate whether or not the FIFO has any free space for writing. In IDT
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
whetherornottheFIFOhasanyfreespaceforwriting.IntheFWFTmode,the
firstwordwrittentoanemptyFIFOgoesdirectlytoQnafterthreeRCLKrising
edges,REN=LOWis notnecessary.Subsequentwords mustbeaccessed
using the Read Enable (REN) and RCLK.
Relevanttimingdiagrams forIDTStandardmodecanbefoundinFigure
11, 12, 13 and 18.
FIRST WORD FALL THROUGH MODE (FWFT)
In this mode, the status flags, IR, PAF, HF, PAE, and OR operate in the
manneroutlinedinTable4.TowritedataintototheFIFO,WENmustbeLOW.
DatapresentedtotheDATAINlineswillbeclockedintotheFIFOonsubsequent
transitionsofWCLK.Afterthefirstwriteisperformed,theOutputReady(OR)
flagwillgoLOW.SubsequentwriteswillcontinuetofilluptheFIFO.PAEwillgo
HIGHaftern + 2wordshavebeenloadedintotheFIFO,wherenistheempty
offsetvalue.Thedefaultsettingforthesevalues arestatedinthefootnoteof
Table2.Thisparameterisalsouserprogrammable.SeesectiononProgram-
mableFlagOffsetLoading.
If one continued to write data into the FIFO, and we assumed no read
operations weretakingplace,theHF wouldtoggletoLOWoncethe8,194th
wordfortheIDT72T7285,16,386thwordfortheIDT72T7295,32,770thword
forthe IDT72T72105and65,538thwordforthe IDT72T72115, respectively
waswrittenintotheFIFO.ContinuingtowritedataintotheFIFOwillcausethe
PAF to go LOW. Again, if no reads are performed, the PAF will go LOW
after (16,385-m) writes for the IDT72T7285, (32,769-m) writes for the
IDT72T7295,(65,537-m)writesfortheIDT72T72105and(131,073-m)writes
fortheIDT72T72115,wheremisthefulloffsetvalue.Thedefaultsettingfor
thesevaluesarestatedinthefootnoteofTable2.
WhentheFIFOisfull,theInputReady(IR)flagwillgoHIGH,inhibitingfurther
writeoperations.Ifnoreadsareperformedafterareset,IRwillgoHIGHafter
DwritestotheFIFO. D =16,385writesfortheIDT72T7285,32,769writesfor
theIDT72T7295,65,537writesfortheIDT72T72105and131,073writesfor
theIDT72T72115,respectively.NotethattheadditionalwordinFWFTmode
isduetothecapacityofthememoryplusoutputregister.
IftheFIFOisfull,thefirstreadoperationwillcausetheIRflagtogoLOW.
Subsequent read operations will cause the PAF and HF to go HIGH at the
conditionsdescribedinTable4.Iffurtherreadoperationsoccur,withoutwrite
operations,thePAEwillgoLOWwhentherearen+1wordsintheFIFO,where
nistheemptyoffsetvalue.ContinuingreadoperationswillcausetheFIFOto
becomeempty.WhenthelastwordhasbeenreadfromtheFIFO,ORwillgo
HIGHinhibitingfurtherreadoperations.RENisignoredwhentheFIFOisempty.
When configured in FWFT mode, the OR flag output is triple register-
buffered,andtheIRflagoutputisdoubleregister-buffered.
Varioussignals,bothinputandoutputsignalsoperatedifferentlydepending
onwhichtimingmodeisineffect.
IDT STANDARD MODE
In this mode, the status flags, FF, PAF, HF, PAE, and EF operate in the
manneroutlinedinTable3.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.ThedefaultsettingforthesevaluesarestatedinthefootnoteofTable2.
Thisparameterisalsouserprogrammable.SeesectiononProgrammableFlag
OffsetLoading.
If one continued to write data into the FIFO, and we assumed no read
operationsweretakingplace,theHalf-Fullflag(HF)wouldtoggletoLOWonce
the8,193rdwordforIDT72T7285,16,385thwordforIDT72T7295,32,769th
wordforIDT72T72105and65,537thwordforIDT72T72115,respectivelywas
written into the FIFO. Continuing to write data into the FIFO will cause the
Programmable Almost-Full flag (PAF) to go LOW. Again, if no reads are
performed,thePAFwillgoLOWafter(16,384-m)writesfortheIDT72T7285,
(32,768-m)writesfortheIDT72T7295,(65,536-m)writesfortheIDT72T72105
and(131,072-m)writes fortheIDT72T72115.Theoffset“m”is thefulloffset
value.ThedefaultsettingforthesevaluesarestatedinthefootnoteofTable2.
Thisparameterisalsouserprogrammable.SeesectiononProgrammableFlag
OffsetLoading.
Relevanttimingdiagrams forFWFTmodecanbefoundinFigure14,15,
16 and 19.
WhentheFIFOisfull,theFullFlag(FF)willgoLOW,inhibitingfurtherwrite
operations.Ifnoreadsareperformedafterareset,FFwillgoLOWafterDwrites
to the FIFO. D = 16,384 writes for the IDT72T7285, 32,768 writes for the
IDT72T7295,65,536writesfortheIDT72T72105and131,072writesforthe
IDT72T72115,respectively.
14
IDT [ INTEGRATED DEVICE TECHNOLOGY ]
