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
operation,whichconsistsofactivatingRENandenablingarisingRCLKedge,
willshiftthewordfrominternalmemorytothedataoutputlines.
InFWFTmode,thefirstwordwrittentoanemptyFIFOisclockeddirectly
tothedataoutputlinesafterthreetransitionsoftheRCLKsignal.ARENdoes
not have to be asserted for accessing the first word. However, subsequent
wordswrittentotheFIFOdorequireaLOWonRENforaccess. Thestateof
theFWFT/SIinputduringMasterResetdeterminesthetimingmodeinuse.
ForapplicationsrequiringmoredatastoragecapacitythanasingleFIFO
canprovide,theFWFTtimingmodepermitsdepthexpansionbychainingFIFOs
inseries(i.e.thedataoutputsofoneFIFOareconnectedtothecorresponding
data inputs of the next). No external logic is required.
These FIFOs have five flagpins, EF/OR (EmptyFlagorOutputReady),
FF/IR (Full Flag or Input Ready), HF (Half-full Flag), PAE (Programmable
Almost-Emptyflag)andPAF(ProgrammableAlmost-Fullflag). TheEFandFF
functions are selected in IDT Standard mode. The IR and OR functions are
selected in FWFT mode. HF, PAE and PAF are always available for use,
irrespectiveoftimingmode.
PAEandPAFcanbeprogrammedindependentlytoswitchatanypointin
memory. Programmableoffsetsdeterminetheflagswitchingthresholdandcan
beloadedbytwomethods:parallelorserial. Eightdefaultoffsetsettingsarealso
provided,sothatPAEcanbesettoswitchatapredefinednumberoflocations
from the empty boundary and the PAF threshold can also be set at similar
predefinedvaluesfromthefullboundary. Thedefaultoffsetvaluesaresetduring
MasterResetbythe state ofthe FSEL0, FSEL1, and LD pins.
For serial programming, SEN together with LD on each rising edge of
SCLK,areusedtoloadtheoffsetregistersviatheSerialInput(SI). Forparallel
programming,WENtogetherwithLDoneachrisingedgeofWCLK,areused
toloadtheoffsetregistersviaDn. RENtogetherwithLDoneachrisingedge
ofRCLKcanbeusedtoreadtheoffsetsinparallelfromQnregardlessofwhether
serialorparalleloffsetloadinghasbeenselected.
DESCRIPTION:
TheIDT72T7285/72T7295/72T72105/72T72115areexceptionallydeep,
extremelyhighspeed,CMOSFirst-In-First-Out(FIFO)memorieswithclocked
read and write controls and a flexible Bus-Matching x72/x36/x18 data flow.
These FIFOs offerseveralkeyuserbenefits:
• Flexible x72/x36/x18 Bus-Matching on both read and write ports
• AuserselectableMARKlocationforretransmit
• User selectable I/O structure for HSTL or LVTTL
• Asynchronous/Synchronous translationonthereadorwriteports
• Thefirstworddatalatencyperiod,fromthetimethefirstwordiswrittentoan
emptyFIFOtothe time itcanbe read, is fixedandshort.
• Highdensityofferingsupto9Mbit
Bus-MatchingTeraSyncFIFOs are particularlyappropriate fornetwork,
video,telecommunications,datacommunicationsandotherapplicationsthat
needtobufferlargeamountsofdataandmatchbussesofunequalsizes.
EachFIFOhas a data inputport(Dn)anda data outputport(Qn), bothof
whichcanassumeeithera72-bit, 36-bitora18-bitwidthasdeterminedbythe
stateofexternalcontrolpinsInputWidth(IW),OutputWidth(OW),andBus-
Matching(BM)pinduringtheMasterResetcycle.
TheinputportcanbeselectedaseitheraSynchronous(clocked)interface,
or Asynchronous interface. During Synchronous operation the input port is
controlledbyaWriteClock(WCLK)inputandaWriteEnable(WEN)input. Data
presentontheDndatainputs is writtenintotheFIFOoneveryrisingedgeof
WCLKwhenWENisasserted.DuringAsynchronousoperationonlytheWR
inputisusedtowritedataintotheFIFO.DataiswrittenonarisingedgeofWR,
theWENinputshouldbetiedtoitsactivestate,(LOW).
TheoutputportcanbeselectedaseitheraSynchronous(clocked)interface,
orAsynchronousinterface.DuringSynchronousoperationtheoutputportis
controlledbyaReadClock(RCLK)inputandReadEnable(REN)input. Data
is read from the FIFO on every rising edge of RCLK when REN is asserted.
DuringAsynchronousoperationonlytheRDinputisusedtoreaddatafromthe
FIFO.Datais readonarisingedgeofRD,theRENinputshouldbetiedtoits
activestate,LOW.WhenAsynchronousoperationisselectedontheoutputport
theFIFOmustbeconfiguredforStandardIDTmode,alsotheRCSshouldbe
tiedLOWandtheOEinputusedtoprovidethree-statecontroloftheoutputs,Qn.
Theoutputportcanbeselectedforeither2.5VLVTTLorHSTLoperation,
thisoperationisselectedbythestateoftheRHSTLinputduringamasterreset.
AnOutputEnable(OE)inputisprovidedforthree-statecontroloftheoutputs.
AReadChipSelect(RCS)inputisalsoprovided,theRCSinputissynchronized
tothereadclock,andalsoprovidesthree-statecontroloftheQndataoutputs.
When RCS is disabled, the data outputs will be high impedance. During
Asynchronousoperationoftheoutputport,RCSshouldbeenabled,heldLOW.
Echo Read Enable, EREN and Echo Read Clock, ERCLK outputs are
provided.Theseareoutputs fromthereadportoftheFIFOthatarerequired
forhighspeeddatacommunication,toprovidetightersynchronizationbetween
thedatabeingtransmittedfromtheQnoutputsandthedatabeingreceivedby
theinputdevice.Datareadfromthereadportisavailableontheoutputbuswith
respect to EREN and ERCLK, this is very useful when data is being read at
highspeed.TheERCLKandERENoutputsarenon-functionalwhentheRead
portissetupforAsynchronousmode.
DuringMasterReset(MRS)thefollowingeventsoccur: thereadandwrite
pointers are set to the first location of the FIFO. The FWFT pin selects IDT
Standardmode orFWFTmode.
The Partial Reset (PRS) also sets the read and write pointers to the first
location of the memory. However, the timing mode, programmable flag
programmingmethod,anddefaultorprogrammedoffsetsettingsexistingbefore
PartialResetremainunchanged.Theflagsareupdatedaccordingtothetiming
modeandoffsetsineffect. PRSisusefulforresettingadeviceinmid-operation,
whenreprogrammingprogrammableflagswouldbeundesirable.
ItisalsopossibletoselectthetimingmodeofthePAE(ProgrammableAlmost-
Empty flag) and PAF (Programmable Almost-Full flag) outputs. The timing
modescanbesettobeeitherasynchronousorsynchronousforthePAEand
PAFflags.
IfasynchronousPAE/PAFconfigurationisselected, thePAEisasserted
LOWontheLOW-to-HIGHtransitionofRCLK.PAEisresettoHIGHontheLOW-
to-HIGHtransitionofWCLK.Similarly,thePAFisassertedLOWontheLOW-
to-HIGHtransitionofWCLKandPAF is resettoHIGHonthe LOW-to-HIGH
transitionofRCLK.
IfsynchronousPAE/PAFconfigurationisselected,thePAEisassertedand
updated on the rising edge of RCLK only and not WCLK. Similarly, PAF is
assertedandupdatedontherisingedgeofWCLKonlyandnotRCLK.Themode
desiredisconfiguredduringMasterResetbythestateoftheProgrammableFlag
Mode (PFM) pin.
ThisdeviceincludesaRetransmitfromMarkfeaturethatutilizestwocontrol
inputs,MARKand,RT(Retransmit).IftheMARKinputisenabledwithrespect
totheRCLK,thememorylocationbeingreadatthatpointwillbemarked.Any
subsequentretransmitoperation,RTgoesLOW,willresetthereadpointerto
this‘marked’location.
ThefrequenciesofboththeRCLKandtheWCLKsignalsmayvaryfrom0
tofMAXwithcompleteindependence. Therearenorestrictionsonthefrequency
oftheoneclockinputwithrespecttotheother.
Therearetwopossibletimingmodesofoperationwiththesedevices:IDT
Standard mode and First Word Fall Through (FWFT) mode.
InIDTStandardmode,thefirstwordwrittentoanemptyFIFOwillnotappear
onthedataoutputlinesunlessaspecificreadoperationisperformed.Aread
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