5
IDT72V201/72V211/72V221/72V231/72V241/72V251 3.3V CMOS SyncFIFO
256 x 9, 512 x 9, 1,024 x 9, 2,048 x 9, 4,096 x 9 and 8,192 x 9
COMMERCIALANDINDUSTRIAL
TEMPERATURERANGES
LD
WEN1
WCLK
Selection
0
Empty Offset (LSB)
Empty Offset (MSB)
Full Offset (LSB)
Full Offset (MSB)
0
1
NoOperation
1
0
Write Into FIFO
1
NoOperation
Figure 2. Write Offset Register
NOTES:
1. For the purposes of this table, WEN2 = VIH.
2. The same selection sequence applies to reading from the registers. REN1 and REN2
are enabled and read is performed on the LOW-to-HIGH transition of RCLK.
SIGNAL DESCRIPTIONS
INPUTS:
DATA IN (D0 - D8)
Data inputs for 9-bit wide data.
CONTROLS:
RESET (RS)
ResetisaccomplishedwhenevertheReset(RS)inputistakentoaLOWstate.
During reset, both internal read and write pointers are set to the first location.
A reset is required after power-up before a write operation can take place. The
Full Flag (FF) and Programmable Almost-Full Flag (PAF) will be reset to HIGH
after tRSF. The Empty Flag (EF) and Programmable Almost-Empty Flag (PAE)
will be reset to LOW after tRSF. During reset, the output register is initialized to
all zeros and the offset registers are initialized to their default values.
WRITE CLOCK (WCLK)
AwritecycleisinitiatedontheLOW-to-HIGHtransitionoftheWriteClock
(WCLK). DatasetupandholdtimesmustbemetinrespecttotheLOW-to-HIGH
transition of the Write Clock (WCLK). The Full Flag (FF) and Programmable
Almost-Full Flag (PAF) are synchronized with respect to the LOW-to-HIGH
transitionoftheWriteClock(WCLK).
The Write and Read clocks can be asynchronous or coincident.
WRITE ENABLE 1 (WEN1)
If the FIFO is configured for programmable flags, Write Enable 1 (WEN1)
istheonlyenablecontrolpin. Inthisconfiguration,whenWriteEnable1(WEN1)
is low, data can be loaded into the input register and RAM array on the LOW-
to-HIGHtransitionofeveryWriteClock(WCLK). DataisstoredintheRAMarray
sequentially and independently of any on-going read operation.
Inthisconfiguration,whenWriteEnable1(WEN1)isHIGH,theinputregister
holdsthepreviousdataandnonewdataisallowedtobeloadedintotheregister.
IftheFIFOisconfiguredtohavetwowriteenables,whichallowsfordepth
expansion,therearetwoenablecontrolpins. SeeWriteEnable2paragraph
belowforoperationinthisconfiguration.
Topreventdataoverflow,theFullFlag(FF)willgoLOW,inhibitingfurther
writeoperations. Uponthecompletionofavalidreadcycle,theFullFlag(FF)
willgoHIGHaftertWFF,allowingavalidwritetobegin. WriteEnable1(WEN1)
is ignored when the FIFO is full.
READ CLOCK (RCLK)
DatacanbereadontheoutputsontheLOW-to-HIGHtransitionoftheRead
Clock(RCLK).TheEmptyFlag(EF)andProgrammableAlmost-EmptyFlag
(PAE)aresynchronizedwithrespecttotheLOW-to-HIGHtransitionoftheRead
Clock (RCLK).
The Write and Read clocks can be asynchronous or coincident.
READ ENABLES (REN1, REN2)
When both Read Enables (REN1, REN2) are LOW, data is read from the
RAM array to the output register on the LOW-to-HIGH transition of the Read
Clock (RCLK).
WheneitherReadEnable(REN1,REN2)isHIGH,theoutputregisterholds
the previous data and no new data is allowed to be loaded into the register.
WhenallthedatahasbeenreadfromtheFIFO,theEmptyFlag(EF)willgo
LOW,inhibitingfurtherreadoperations.Onceavalidwriteoperationhasbeen
accomplished,theEmptyFlag(EF)willgoHIGHaftertREFandavalidreadcan
begin. TheReadEnables(REN1,REN2)areignoredwhentheFIFOisempty.
OUTPUT ENABLE (OE)
When Output Enable (OE) is enabled (LOW), the parallel output buffers
receive data from the output register. When Output Enable (OE) is disabled
(HIGH), the Q output data bus is in a high-impedance state.
WRITE ENABLE 2/LOAD (WEN2/LD)
This is a dual-purpose pin. The FIFO is configured at Reset to have
programmableflagsortohavetwowriteenables,whichallowsdepthexpansion.
If Write Enable 2/Load (WEN2/LD) is set high at Reset (RS = LOW), this pin
operates as a second Write Enable pin.
If the FIFO is configured to have two write enables, when Write Enable
(WEN1) is LOW and Write Enable 2/Load (WEN2/LD) is HIGH, data can be
loaded into the input register and RAM array on the LOW-to-HIGH transition
ofeveryWriteClock(WCLK). DataisstoredintheRAMarraysequentiallyand
independently of any on-going read operation.
In this configuration, when Write Enable (WEN1) is HIGH and/or Write
Enable2/Load(WEN2/LD)isLOW,theinputregisterholdsthepreviousdata
and no new data is allowed to be loaded into the register.
Topreventdataoverflow,theFullFlag(FF)willgoLOW,inhibitingfurther
writeoperations. Uponthecompletionofavalidreadcycle,theFullFlag(FF)
willgoHIGHaftertWFF,allowingavalidwritetobegin. WriteEnable1(WEN1)
and Write Enable 2/Load (WEN2/LD) are ignored when the FIFO is full.
TheFIFOisconfiguredtohaveprogrammableflagswhentheWriteEnable
2/Load(WEN2/LD)issetLOWatReset(RS =LOW). TheIDT72V201/72V211/
72V221/72V231/72V241/72V251 devices contain four 8-bit offset registers
whichcanbeloadedwithdataontheinputs,orreadontheoutputs. SeeFigure
3 for details of the size of the registers and the default values.
If theFIFOisconfiguredtohaveprogrammableflagswhentheWriteEnable
1(WEN1)andWriteEnable2/Load(WEN2/LD)aresetlow,dataontheinputs
DiswrittenintotheEmpty(LeastSignificantBit)OffsetregisteronthefirstLOW-
to-HIGHtransitionoftheWriteClock(WCLK). DataiswrittenintotheEmpty(Most
SignificantBit)OffsetregisteronthesecondLOW-to-HIGHtransitionoftheWrite
Clock (WCLK), into the Full (Least Significant Bit) Offset register on the third
transition, and into the Full (Most Significant Bit) Offset register on the fourth
transition. Thefifth transitionofthe WriteClock(WCLK)againwritestotheEmpty
(LeastSignificantBit)Offsetregister.
However,writingalloffsetregistersdoesnothavetooccuratonetime. One
ortwooffsetregisterscanbewrittenandthenbybringingtheWriteEnable2/
Load (WEN2/LD) pin HIGH, the FIFO is returned to normal read/write
operation. WhentheWriteEnable2/Load(WEN2/LD)pinissetLOW,andWrite
Enable 1 (WEN1) is LOW, the next offset register in sequence is written.
Thecontentsoftheoffsetregisterscanbereadontheoutputlineswhenthe
WriteEnable2/Load(WEN2/LD)pinissetlowandbothReadEnables(REN1,
REN2) are set LOW. Data can be read on the LOW-to-HIGH transition of the
Read Clock (RCLK).
A read and write should not be performed simultaneously to the offset
registers.