6

COMMERCIAL,INDUSTRIALANDMILITARY

TEMPERATURERANGES

IDT7201L/7201LA/7202LA CMOS ASYNCHRONOUS FIFO

256 x 9, 512 x 9 and 1,024 x 9

DeviceMode,thispinactsastheretransmitinput. TheSingleDeviceModeis

initiated by grounding the Expansion In (XI).

The IDT7200/7201A/7202A can be made to retransmit data when the

RetransmitEnablecontrol(RT)inputispulsedLOW. Aretransmitoperationwill

settheinternalreadpointertothefirstlocationandwillnotaffectthewritepointer.

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

retransmit. This feature is useful when less than 256/512/1,024 writes are

performedbetweenresets. Theretransmitfeatureisnotcompatiblewiththe

Depth 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

device is full. If the read pointer is not moved after Reset (RS), the Full-Flag

(FF)willgoLOWafter256writesforIDT7200,512writesfortheIDT7201Aand

1,024 writes for the IDT7202A.

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

Expansion In (XI) is grounded, this output acts as an indication of a half-full

memory.

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

to one half of the total memory of the device. The Half-Full Flag (HF) is then

reset 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.

Dataoutputsfor9-bitwidedata. Thisdataisinahighimpedancecondition

whenever Read (R) is in a HIGH state.

SIGNAL DESCRIPTIONS

INPUTS:

Data inputs for 9-bit wide data.

CONTROLS:

RESET (RS)

Reset is accomplished whenever the Reset (RS) input is taken to a LOW

state. 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. Both the Read Enable (R) and Write Enable (W) inputs must be

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

isfull,theinternalwritepointerisblockedfromW,soexternalchangesinWwill

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

thenextReadoperation. WhenalldatahasbeenreadfromtheFIFO,theEmpty

Flag(EF)willgoLOW,allowingthe“final”readcyclebutinhibitingfurtherread

operationswiththedataoutputsremaininginahighimpedancestate. Oncea

validwriteoperationhasbeenaccomplished,theEmptyFlag(EF)willgoHIGH

readpointerisblockedfromRsoexternalchangesinRwillnotaffecttheFIFO

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