10
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
When the LD pin is LOW and WEN is HIGH, the WCLK input is disabled;
thenasignalatthisinputcanneitherincrementthewriteoffsetregisterpointer,
nor execute a write.
The contents of the offset registers can be read on the output lines when
theLDpinissetLOWandRENissetLOW;then,datacanbereadontheLOW-
to-HIGH transition of the Read Clock (RCLK). The act of reading the control
registersemploysadedicatedreadoffsetregisterpointer.(Thereadandwrite
pointersoperateindependently). Offsetregistercontentcanbereadoutinthe
IDT Standard mode only. It is inhibited in the FWFT mode.
A read and a write should not be performed simultaneously to the offset
registers.
FIRST LOAD (FL)
Forthesingledevicemode,seeTable3foradditionalinformation. Inthe
DaisyChainDepthExpansionconfiguration,FLisgroundedtoindicateitisthe
firstdeviceloadedandissettoHIGHforallotherdevicesintheDaisyChain.
(SeeOperatingConfigurationsforfurtherdetails.)
WRITE EXPANSION INPUT (WXI)
This is a dual purpose pin. For single device mode, see Table 3 for
additionalinformation. WXIisconnectedtoWriteExpansionOut(WXO)ofthe
previous device in the Daisy Chain Depth Expansion mode.
READ EXPANSION INPUT (RXI)
This is a dual purpose pin. For single device mode, see Table 3 for
additionalinformation.RXIisconnectedtoReadExpansionOut(RXO)ofthe
previous device in the Daisy Chain Depth Expansion mode.
OUTPUTS:
FULL FLAG/INPUT READY (FF/IR)
This is a dual purpose pin. In IDT Standard mode, the Full Flag (FF)
functionisselected.WhentheFIFOisfull,FFwillgoLOW,inhibitingfurtherwrite
operations. WhenFFisHIGH,theFIFOisnotfull. Ifnoreadsareperformed
afterareset,FF willgoLOWafterDwritestotheFIFO. D=256writesforthe
IDT72V205,512fortheIDT72V215,1,024fortheIDT72V225,2,048forthe
IDT72V235 and 4,096 for the IDT72V245.
In FWFT mode, the Input Ready (IR) function is selected. IR goes LOW
whenmemoryspaceisavailableforwritingindata. When thereisnolonger
any free space left, IR goes HIGH, inhibiting further write operations.
IRwillgoHIGHafterDwritestotheFIFO. D=257writesfortheIDT72V205,
513 for the IDT72V215, 1,025 for the IDT72V225, 2,049 for the IDT72V235
and 4,097 for the IDT72V245. Note that the additional word in FWFT mode
is due to the capacity of the memory plus output register.
FF/IR is synchronous and updated on the rising edge of WCLK.
EMPTYFLAG/OUTPUTREADY(EF/OR)
Thisisadualpurposepin. IntheIDTStandardmode,theEmptyFlag(EF)
functionisselected. WhentheFIFOisempty,EFwillgoLOW,inhibitingfurther
read operations. When EF is HIGH, the FIFO is not empty.
InFWFTmode,theOutputReady(OR)functionisselected.ORgoesLOW
atthesametimethatthefirstwordwrittentoanemptyFIFOappearsvalidon
theoutputs. ORstaysLOWaftertheRCLKLOWtoHIGHtransitionthatshifts
thelastwordfromtheFIFOmemorytotheoutputs. ORgoesHIGHonlywith
atrueread(RCLKwithREN=LOW). Thepreviousdatastaysattheoutputs,
indicating the last word was read. Further data reads are inhibited until OR
goesLOWagain.
EF/OR is synchronous and updated on the rising edge of RCLK.
PROGRAMMABLE ALMOST-FULL FLAG (PAF)
The Programmable Almost-Full Flag (PAF) will go LOW when FIFO
reaches the almost-full condition. In IDT Standard mode, if no reads are
performed after Reset (RS), the PAF will go LOW after (256-m) writes for the
IDT72V205, (512-m) writes for the IDT72V215, (1,024-m) writes for the
IDT72V225,(2,048–m)writesfortheIDT72V235and(4,096–m)writesforthe
IDT72V245. The offset “m” is defined in the Full Offset register.
In FWFT mode, if no reads are performed, PAF will go LOW after 257-m
fortheIDT72V205,513-mfortheIDT72V215,1,025fortheIDT72V225,2,049
fortheIDT72V235and4,097fortheIDT72V245.Thedefaultvaluesformare
noted in Table 1 and 2.
IfasynchronousPAFconfigurationisselected,thePAFisassertedLOW
ontheLOW-to-HIGHtransitionoftheWriteClock(WCLK). PAFisresettoHIGH
ontheLOW-to-HIGHtransitionoftheReadClock(RCLK).IfsynchronousPAF
configurationisselected(seeTable3),thePAFisupdatedontherisingedge
ofWCLK.
PROGRAMMABLEALMOST-EMPTYFLAG(PAE)
The PAE flag will go LOW when the FIFO reaches the almost-empty
condition. In IDT Standard mode, PAE will go LOW when there are n words
orlessintheFIFO. InFWFTmode,thePAEwillgoLOWwhentherearen + 1
wordsorlessintheFIFO.Theoffset"n"isdefinedastheemptyoffset. Thedefault
values for n are noted in Table 1 and 2.
Ifthereisnoemptyoffsetspecified,theProgrammableAlmost-EmptyFlag
(PAE) will be LOW when the device is 31 away from completely empty for
IDT72V205, 63 away from completely empty for IDT72V215, and 127 away
fromcompletelyemptyforIDT72V225/72V235/72V245.
IfasynchronousPAEconfigurationisselected,thePAEisassertedLOWon
theLOW-to-HIGHtransitionoftheReadClock(RCLK).PAEisresettoHIGH
ontheLOW-to-HIGHtransitionoftheWriteClock(WCLK).IfsynchronousPAE
configurationisselected(seeTable3),the PAEisupdatedontherisingedge
of RCLK.
WRITE EXPANSION OUT/HALF-FULL FLAG (WXO/HF)
This is a dual-purpose output. In the Single Device and Width Expansion
mode, when Write Expansion In (WXI) and/or Read Expansion In (RXI) are
grounded,thisoutputactsasanindicationofahalf-fullmemory.
Afterhalfofthememoryisfilled,andattheLOW-to-HIGHtransitionofthenext
writecycle,theHalf-FullFlaggoesLOWandwillremainsetuntilthedifference
between the write pointer and read pointer is less than or equal to one half of
the total memory of the device. The Half-Full Flag (HF) is then reset to HIGH
by the LOW-to-HIGH transition of the Read Clock (RCLK). The HF is
asynchronous.
In the Daisy Chain Depth Expansion mode, WXI is connected to WXO of
thepreviousdevice. ThisoutputactsasasignaltothenextdeviceintheDaisy
Chainbyprovidingapulsewhenthepreviousdevicewritestothelastlocation
ofmemory.
READ EXPANSION OUT (RXO)
In the Daisy Chain Depth Expansion configuration, Read Expansion In
(RXI)isconnectedtoReadExpansionOut(RXO)ofthepreviousdevice.This
outputactsasasignaltothenextdeviceintheDaisyChainbyprovidingapulse
when the previous device reads from the last location of memory.
DATAOUTPUTS(Q0-Q17)
Q0-Q17 are data outputs for 18-bit wide data.