IDT7204 datasheet(6/14 Pages) IDT

6 / 14 page

COMMERCIAL,INDUSTRIALANDMILITARY

TEMPERATURERANGES

IDT7203/7204/7205/7206/7207/7208 CMOS ASYNCHRONOUS FIFO

2,048 x 9, 4,096 x 9, 8,192 x 9, 16,384 x 9, 32,768 x 9 and 65,536 x 9

loaded(seeOperatingModes).TheSingleDeviceModeisinitiatedbygrounding

the Expansion In (XI).

TheIDT7203/7204/7205/7206/7207/7208canbemadetoretransmitdata

when the Retransmit Enable Control (RT) input is pulsed LOW. A retransmit

operationwillsettheinternalreadpointertothefirstlocationandwillnotaffectthe

writepointer. ThestatusoftheFlagswillchangedependingontherelativelocations

of the read and write pointers. Read Enable (R) and Write Enable (W) must be

intheHIGHstateduringretransmit. Thisfeatureisusefulwhenlessthan2,048/

4,096/8,192/16,384/32,768/65,536writesareperformedbetweenresets. The

retransmitfeatureisnotcompatiblewiththeDepthExpansionMode.

EXPANSION IN ( XI ) — This input is a dual-purpose pin. Expansion In (XI)

isgroundedtoindicateanoperationinthesingledevicemode. ExpansionIn(XI)

isconnectedtoExpansionOut(XO)ofthepreviousdeviceintheDepthExpansion

or Daisy-Chain Mode.

OUTPUTS:

FULL FLAG

(FF)—TheFullFlag(FF)willgoLOW,inhibitingfurtherwrite

operations,whenthedeviceisfull. IfthereadpointerisnotmovedafterReset(RS),

the Full Flag (FF) will go LOW after 2,048/4,096/8,192/16,384/32,768/65,536

writes.

EMPTY FLAG ( EF ) — The Empty Flag (EF) will go LOW, inhibiting further

readoperations,whenthereadpointerisequaltothewritepointer,indicatingthat

thedeviceisempty.

EXPANSIONOUT/HALF-FULLFLAG(XO/HF)—Thisisadual-purpose

output. Inthesingledevicemode,whenExpansionIn(XI)isgrounded,thisoutput

actsasanindicationofahalf-fullmemory.

Afterhalfofthememoryisfilled,andatthefallingedgeofthenextwriteoperation,

the Half-Full Flag (HF) will be set to LOW and will remain set until the difference

betweenthewritepointerandreadpointerislessthanorequaltoonehalfofthe

totalmemoryofthedevice. TheHalf-FullFlag(HF)isthenresetbytherisingedge

of the read operation.

IntheDepthExpansionMode,ExpansionIn(XI)isconnectedtoExpansion

Out (XO) of the previous device. This output acts as a signal to the next device

intheDaisyChainbyprovidingapulsetothenextdevicewhenthepreviousdevice

reaches the last location of memory. There will be an XO pulse when the Write

pointerreachesthelastlocationofmemory,andanadditionalXOpulsewhenthe

Readpointerreachesthelastlocationofmemory.

DATA OUTPUTS (Q0-Q8) — Q0-Q8 are data outputs for 9-bit wide data.

Theseoutputsareinahigh-impedanceconditionwheneverRead(R)isinaHIGH

state.

SI GN AL DESCRI PT I ON S

INPUTS:

DATA IN (D0–D8)

— Data inputs for 9-bit wide data.

CONTROLS:

RESET ( RS ) — Reset is accomplished whenever the Reset (RS) input is

takentoaLOWstate. Duringreset,bothinternalreadandwritepointersareset

tothefirstlocation.Aresetisrequiredafterpower-upbeforeawriteoperationcan

take place. 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.

WRITE ENABLE ( W ) — A write cycle is initiated on the falling edge of this

inputiftheFullFlag(FF)isnotset.Dataset-upandholdtimesmustbeadhered-

to,withrespecttotherisingedgeoftheWriteEnable(W).DataisstoredintheRAM

array sequentially and independently of any on-going read operation.

Afterhalfofthememoryisfilled,andatthefallingedgeofthenextwriteoperation,

theHalf-FullFlag(HF)willbesettoLOW,andwillremainsetuntilthedifference

betweenthewritepointerandreadpointerisless-thanorequaltoone-halfofthe

totalmemoryofthedevice.TheHalf-FullFlag(HF)isthenresetbytherisingedge

of the read operation.

To prevent data overflow, the Full Flag (FF) will go LOW on the falling edge

ofthelastwritesignal,whichinhibitsfurtherwriteoperations. Uponthecompletion

of a valid read operation, the Full Flag (FF) will go HIGH after tRFF, allowing a

newvalidwritetobegin.WhentheFIFOisfull,theinternalwritepointerisblocked

from W, so external changes in W will not affect the FIFO when it is full.

READENABLE(R)—A readcycleisinitiatedonthefallingedgeoftheRead

Enable (R), provided the Empty Flag (EF) is not set. The data is accessed on

aFirst-In/First-Outbasis,independentofanyongoingwriteoperations. AfterRead

Enable (R) goes HIGH, the Data Outputs (Q0 through Q8) will return to a high-

impedanceconditionuntilthenextReadoperation. Whenallthedatahasbeen

read from the FIFO, the Empty Flag (EF) will go LOW, allowing the “final” read

cyclebutinhibitingfurtherreadoperations,withthedataoutputsremaininginahigh-

impedancestate.Onceavalidwriteoperationhasbeenaccomplished,theEmpty

Flag (EF) will go HIGH after tWEF and a valid Read can then begin. When the

FIFOisempty,theinternalreadpointerisblockedfromRsoexternalchangeswill

notaffecttheFIFOwhenitisempty.

FIRST LOAD/RETRANSMIT ( FL/RT

) — This is a dual-purpose input. In

theDepthExpansionMode,thispinisgroundedtoindicatethatitisthefirstdevice

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