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COMMERCIALTEMPERATURERANGE

IDT7280/7281/7282/7283/7284/7285 5V ASYNCHRONOUS FIFO

DUAL 256 x 9, 512 x 9, 1,024 x 9, 2,048 x 9, 4,096 x 9 and 8,192 x 9

JUNE 29, 2012

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.

Aresetisrequiredafterpowerupbeforeawriteoperationcantakeplace.Both

the Read Enable (R) and Write Enable (W) inputs must be in the HIGH

state during the window shown in Figure 2, (i.e., tRSS before the rising

edge of RS) and should not change until tRSR after the rising edge of

RS. Half-Full Flag (HF) will be reset to HIGH after Reset (RS).

WRITE ENABLE (W)

A write cycle is initiated on the falling edge of this input if the Full Flag (FF)

isnotset.Dataset-upandholdtimesmustbeadheredtowithrespecttotherising

edgeoftheWriteEnable(W).DataisstoredintheRAMarraysequentiallyand

independently of any on-going read operation.

After half of the memory is filled and at the falling edge of the next write

operation,theHalf-FullFlag(HF)willbesettoLOWandwillremainsetuntilthe

difference between the write pointer and read pointer is less than or equal to

onehalfofthetotalmemoryofthedevice.TheHalf-FullFlag(HF)isthenreset

by the rising edge of the read operation.

Topreventdataoverflow,theFullFlag(FF)willgoLOW,inhibitingfurther

write operations. Upon the completion of a valid read operation, the Full Flag

(FF) will go HIGH after tRFF, allowing a valid write to begin. When the FIFO is

full, the internal write pointer is blocked from W, so external changes in Wwill

notaffecttheFIFOwhenitisfull.

READ ENABLE (R)

AreadcycleisinitiatedonthefallingedgeoftheReadEnable(R)provided

theEmptyFlag(EF)isnotset.ThedataisaccessedonaFirst-In/First-Outbasis,

independent of any ongoing write operations. After Read Enable (R) goes

HIGH,theDataOutputs(Q0–Q8)willreturntoahighimpedanceconditionuntil

thenextReadoperation.WhenalldatahasbeenreadfromtheFIFO,theEmpty

Flag (EF) will go LOW, allowing the “final” read cycle but inhibiting further read

operations with the data outputs remaining in a high impedance state. Once a

valid write operation has been accomplished, the Empty Flag (EF)willgoHIGH

aftertWEFandavalidReadcanthenbegin.WhentheFIFOisempty,theinternal

read pointer is blocked from Rso external changes in Rwill not affect the FIFO

when it is empty.

FIRST LOAD/RETRANSMIT (FL/RT)

This is a dual-purpose input. In the Depth Expansion Mode, this pin is

groundedtoindicatethatitisthefirstloaded(seeOperatingModes). IntheSingle

DeviceMode,thispinactsastheretransmitinput.TheSingleDeviceModeis

initiated by grounding the Expansion In (XI).

ThesedevicescanbemadetoretransmitdatawhentheRetransmitEnable

control(RT)inputispulsedLOW. Aretransmitoperationwillsettheinternalread

pointertothefirstlocationandwillnotaffectthewritepointer.ReadEnable(R)

andWriteEnable(W)mustbeintheHIGHstateduringretransmit.Thisfeature

is useful when less than 256/512/1,024/2,048/4,096/8,192 writes are per-

formedbetweenresets.TheretransmitfeatureisnotcompatiblewiththeDepth

Expansion Mode and will affect the Half-Full Flag (HF), depending on the

relative locations of the read and write pointers.

EXPANSION IN (XI)

Thisinputisadual-purposepin. ExpansionIn(XI)isgroundedtoindicate

an operation in the single device mode. Expansion In (XI) is connected to

Expansion Out (XO) of the previous device in the Depth Expansion or Daisy

Chain Mode.

OUTPUTS:

FULL FLAG (FF)

TheFullFlag(FF)willgoLOW,inhibitingfurtherwriteoperation,whenthe

write pointer is one location less than the read pointer, indicating that the

deviceisfull.IfthereadpointerisnotmovedafterReset(RS),theFull-Flag(FF)

will go LOW after 256 writes for IDT7280, 512 writes for the IDT7281, 1,024

writes for the IDT7282, 2,048 writes for the IDT7283, 4,096 writes for the

IDT7284 and 8,192 writes for the IDT7285.

EMPTY FLAG (EF)

TheEmptyFlag(EF)willgoLOW,inhibitingfurtherreadoperations,when

the read pointer is equal to the write pointer, indicating that the device is

empty.

EXPANSION OUT/HALF-FULL FLAG (XO/HF)

This is a dual-purpose output. In the single device mode, when Expan-

sionIn(XI)isgrounded,thisoutputactsasanindicationofahalf-fullmemory.

After half of the memory is filled and at the falling edge of the next write

operation,theHalf-FullFlag(HF)willbesetLOWandwillremainsetuntilthe

difference between the write pointer and read pointer is less than or equal

toonehalfofthetotalmemoryofthedevice.TheHalf-FullFlag(HF)isthenreset

by using rising edge of the read operation.

IntheDepthExpansionMode,ExpansionIn(XI)isconnectedtoExpansion

Out(XO)ofthepreviousdevice.Thisoutputactsasasignaltothenextdevice

in the Daisy Chain by providing a pulse to the next device when the previous

devicereachesthelastlocationofmemory.

DATA OUTPUTS (Q0 – Q8)

Data outputs for 9-bit wide data. This data is in a high impedance

condition whenever Read (R) is in a HIGH state.