4

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

SIGNAL DESCRIPTIONS

INPUTS:

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.Both

the Read Enable (

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

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

edge of the Write Enable (

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, the Half-Full Flag (

HF)willbesettoLOWandwillremainsetuntilthe

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)isthenreset

by the rising edge of the read operation.

To prevent data overflow, the Full Flag (

FF) will go LOW, inhibiting further

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

(

full, the internal write pointer is blocked from

W, so external changes in Wwill

not affect the FIFO when it is full.

READ ENABLE (

R)

A read cycle is initiated on the falling edge of the Read Enable (

R)provided

the Empty Flag (

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

independent of any ongoing write operations. After Read Enable (

R) goes

the next Read operation. When all data has been read from the FIFO, the Empty

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) will go HIGH

read pointer is blocked from

Rso external changes in R will 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

Device Mode, this pin acts as the retransmit input. The Single Device Mode is

initiated by grounding the Expansion In (

XI).

ThesedevicescanbemadetoretransmitdatawhentheRetransmitEnable

control(

RT)inputispulsedLOW. Aretransmitoperationwillsettheinternalread

pointer to the first location and will not affect the write pointer. Read Enable (

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)

This input is a dual-purpose pin. Expansion In (

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)

The Full Flag (

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)

The Empty Flag (

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-

sion In (

XI)isgrounded,thisoutputactsasanindicationofahalf-fullmemory.

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

operation, the Half-Full Flag (

HF) will be set LOW and will remain set until the

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

device reaches the last location of memory.

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

condition whenever Read (

R) is in a HIGH state.