IDT72801/728211/72821/72831/72841/72851 DUAL CMOS SyncFIFOTM
DUAL 256 x 9, DUAL 512 x 9, DUAL 1K x 9, DUAL 2K x 9, DUAL 4K x 9, DUAL 8K x 9
COMMERCIAL AND INDUSTRIAL
TEMPERATURERANGES
When either of the two Read Enable RENA1, RENA2 (RENB1, RENB2)
associatedwithFIFOA(B)isHIGH,theoutputregisterholdsthepreviousdata
and no new data is allowed to be loaded into the register.
WhenallthedatahasbeenreadfromFIFOA(B),theEmptyFlagEFA(EFB)
willgoLOW,inhibitingfurtherreadoperations. Onceavalidwriteoperationhas
beenaccomplished,EFA(EFB)willgoHIGHaftertREFandavalidreadcan
begin. TheReadEnablesRENA1,RENA2(RENB1,RENB2)areignoredwhen
FIFO A (B) is empty.
SIGNALDESCRIPTIONS
FIFOAandFIFOBareidenticalineveryrespect.Thefollowingdescription
explainstheinteractionofinputandoutputsignalsforFIFOA.Thecorrespond-
ing signal names for FIFO B are provided in parentheses.
INPUTS:
Data In (DA0 – DA8, DB0 – DB8) — DA0 - DA8 are the nine data inputs
for memory array A. DB0 - DB8 are the nine data inputs for memory array B.
OutputEnable(OEA,OEB)—WhenOutputEnableOEA(OEB)isenabled
(LOW),theparalleloutputbuffersofFIFOA(B)receivedatafromtheirrespective
outputregister. WhenOutputEnable OEA(OEB)isdisabled(HIGH),theQA
(QB)outputdatabusisinahigh-impedancestate.
CONTROLS:
Reset(RSA,RSB)—ResetofFIFOA(B)isaccomplishedwheneverRSA
(RSB)inputistakentoaLOWstate.DuringReset,theinternalreadandwrite
pointersassociatedwiththeFIFOaresettothefirstlocation.AResetisrequired
afterpower-upbeforeawriteoperationcantakeplace. TheFullFlagFFA(FFB)
andProgrammableAlmost-FullflagPAFA(PAFB)willberesettoHIGHafter
tRSF. TheEmptyFlagEFA(EFB)andProgrammableAlmost-EmptyflagPAEA
(PAEB) will be reset to LOW after tRSF. During Reset, the output register is
initializedtoallzerosandtheoffsetregistersareinitializedtotheirdefaultvalues.
Write Enable 2/Load (WENA2/LDA, WENB2/LDB) — This is a dual-
purpose pin. FIFOA(B)is configuredatResettohave programmable flags
ortohavetwowriteenables,whichallows depthexpansion. IfWENA2/LDA
(WENB2/LDB) issetHIGHatResetRSA=LOW(RSB = LOW),thispinoperates
as a second write enable pin.
If FIFO A (B) is configured to have two write enables, when Write Enable
1WENA1(WENB1)isLOWandWENA2/LDA(WENB2/LDB)isHIGH,datacanbe
loaded into the input register and RAM array on the LOW-to-HIGH transition
ofeveryWriteClockWCLKA(WCLKB). Dataisstoredinthearraysequentially
and independently of any ongoing read operation.
Write Clock (WCLKA, WCLKB) — A write cycle to Array A (B) is
initiated on the LOW-to-HIGH transition of WCLKA (WCLKB). Data setup
and hold times must be met with respect to the LOW-to-HIGH transition of
WCLKA(WCLKB). TheFullFlagFFA (FFB)andProgrammableAlmost-Full
flagPAFA(PAFB)aresynchronizedwithrespecttotheLOW-to-HIGHtransition
oftheWriteClockWCLKA(WCLKB).
Inthisconfiguration,whenWENA1(WENB1)isHIGHand/orWENA2/LDA
(WENB2/LDB)isLOW,theinputregisterofArrayAholdsthepreviousdataand
no new data is allowed to be loaded into the register.
Topreventdata overflow, the FullFlagFFA (FFB)willgoLOW, inhibiting
furtherwriteoperations. Uponthecompletionofavalidreadcycle,FFA(FFB)
willgoHIGHaftertWFF,allowingavalidwritetobegin. WENA1,(WENB1)and
WENA2/LDA (WENB2/LDB)are ignoredwhenthe FIFOis full.
FIFOA(B)is configuredtohave programmable flags whenthe WENA2/
LDA(WENB2/LDB)issetLOWatResetRSA = LOW(RSB=LOW). EachFIFO
containsfour8-bitoffsetregisterswhichcanbeloadedwithdataontheinputs,
orreadontheoutputs. SeeFigure3fordetailsofthesizeoftheregistersand
thedefaultvalues.
IfFIFOA(B)is configuredtohave programmable flags, whenthe WENA1
(WENB1) and WENA2/LDA (WENB2/LDB) are set LOW, data on the DA (DB)
inputsarewrittenintotheEmpty(LeastSignificantBit)Offsetregisteronthefirst
LOW-to-HIGH transition of the WCLKA (WCLKB). Data are written into the
Empty (Most Significant Bit) Offset register on the second LOW-to-HIGH
transitionofWCLKA(WCLKB),intotheFull(LeastSignificantBit)Offsetregister
onthethirdtransition,andintotheFull(MostSignificantBit)Offsetregisteron
thefourthtransition. ThefifthtransitionofWCLKA(WCLKB)againwritestothe
Empty(LeastSignificantBit)Offsetregister.
The Write and Read Clocks can be asynchronous or coincident.
Write Enable 1 (WENA1, WENB1) — If FIFO A (B) is configured for
programmable flags, WENA1 (WENB1) is the only enable control pin. In this
configuration,whenWENA1(WENB1)isLOW,datacanbeloadedintotheinput
registerofRAMArrayA(B)ontheLOW-to-HIGHtransitionofeveryWriteClock
WCLKA(WCLKB). DataisstoredinArrayA(B)sequentiallyandindependently
of any ongoing read operation.
Inthisconfiguration,whenWENA1(WENB1)isHIGH,theinputregisterholds
the previous data and no new data is allowed to be loaded into the register.
IftheFIFOisconfiguredtohavetwowriteenables,whichallowsfordepth
expansion. See Write Enable 2 paragraph below for operation in this
configuration.
To prevent data overflow, FFA (FFB) will go LOW, inhibiting further write
operations. Uponthecompletionofavalidreadcycle,theFFA(FFB)willgoHIGH
aftertWFF,allowingavalidwritetobegin. WENA1(WENB1)isignoredwhenFIFO
A (B) is full.
However,writingalloffsetregistersdoesnothavetooccuratonetime. One
ortwooffsetregisterscanbewrittenandthenbybringingLDA(LDB)HIGH,FIFO
A(B)is returnedtonormalread/write operation. WhenLDA (LDB)is setLOW,
andWENA1(WENB1)isLOW,thenextoffsetregisterinsequenceiswritten.
ThecontentsoftheoffsetregisterscanbereadontheQA(QB)outputs when
WENA2/LDA(WENB2/LDB)issetLOWandbothReadEnablesRENA1,RENA2
(RENB1,RENB2)aresetLOW. DatacanbereadontheLOW-to-HIGHtransition
of the Read Clock RCLKA (RCLKB).
ReadClock(RCLKA, RCLKB)—Data canbe readfromArrayA(B)on
theLOW-to-HIGHtransitionofRCLKA(RCLKB). TheEmptyFlagEFA(EFB)
andProgrammableAlmost-EmptyFlagPAEA(PAEB)aresynchronizedwith
respecttotheLOW-to-HIGHtransitionof RCLKA(RCLKB).
The Write and Read Clocks can be asynchronous or coincident.
Read Enables (RENA1, RENA2, RENB1, RENB2) — When both Read
Enables RENA1,RENA2 (RENB1,RENB2)are LOW, data is readfromArray
A(B)totheoutputregisterontheLOW-to-HIGHtransitionoftheReadClock
RCLKA (RCLKB).
6
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