10

COMMERCIALTEMPERATURERANGE

2,048 x 36 x 2, 4,096 x 36 x 2 and 8,192 x 36 x 2

read request necessary. Subsequent words must be accessed by performing

a formal read operation.

Following Reset, the level applied to the

FWFTinputtochoosethedesired

timing mode must remain static throughout FIFO operation. Refer to Figure 2

(Reset) for a First Word Fall Through select timing diagram.

ALMOST-EMPTYFLAGANDALMOST-FULLFLAGOFFSETPROGRAMMING

Four registers in these devices are used to hold the offset values for the

Almost-EmptyandAlmost-Fullflags. TheportBAlmost-Emptyflag(

AEB)Offset

register is labeled X1 and the port A Almost-Empty flag (

AEA)Offsetregisteris

labeled X2. The port A Almost-Full flag (

AFA)OffsetregisterislabeledY1and

theportBAlmost-Fullflag(

AFB)OffsetregisterislabeledY2. Theindexofeach

register name corresponds to its FIFO number. The offset registers can be

loadedwithpresetvaluesduringtheresetofaFIFOortheycanbeprogrammed

from port A (see Table 1).

FS0andFS1functionthesamewayinbothIDTStandardandFWFTmodes.

— PRESET VALUES

ToloadtheFIFO'sAlmost-EmptyflagandAlmost-FullflagOffsetregisterswith

oneofthethreepresetvalueslistedinTable1,atleastoneoftheflagselectinputs

mustbeHIGHduringtheLOW-to-HIGHtransitionofitsresetinput. Forexample,

to load the preset value of 64 into X1 and Y1, FS0 and FS1 must be HIGH when

FlFO1Reset(

RST1)returnsHIGH. FlagoffsetregistersassociatedwithFIFO2

are loaded with one of the preset values in the same way with FIFO2 Reset

(

RST2) toggled simultaneously with FIFO1 Reset (RST1). For preset value

loading timing diagram, see Figure 2.

— PARALLEL LOAD FROM PORT A

To program the X1, X2, Y1, and Y2 registers from port A, both FlFOs should

be reset simultaneously with FS0 and FS1 LOW during the LOW-to-HIGH

transitionoftheResetinputs. Itisimportanttonotethatonceparallelprogramming

hasbeenselectedduringaMasterResetbyholdingbothFS0&FS1LOW,these

inputsmustremainLOWduringallsubsequentFIFOoperation. Theycanonly

be toggled HIGH when future Master Resets are performed and other

programming methods are desired.

After this reset is complete, the first four writes to FIFO1 do not store data in

the FIFO memory but load the offset registers in the order Y1, X1, Y2, X2. The

port A data inputs used by the offset registers are (A7-A0), (A8-A0), or (A9-A0)

SIGNAL DESCRIPTION

RESET

After power up, a Master Reset operation must be performed by providing

a LOW pulse to

RST1 and RST2 simultaneously. Afterwards, the FIFO

memories of the IDT723652/723662/723672 are reset separately by taking

theirReset(

RST1,RST2)inputsLOWforatleastfourport-AClock(CLKA)and

four port-B Clock (CLKB) LOW-to-HIGH transitions. The Reset inputs can

switch asynchronously to the clocks. A FIFO reset initializes the internal read

and write pointers and forces the Input Ready flag (IRA, IRB) LOW, the Output

Ready flag (ORA, ORB) LOW, the Almost-Empty flag (

AEA, AEB) LOW, and

theAlmost-Fullflag(

AFA,AFB)HIGH. ResettingaFIFOalsoforcestheMailbox

Flag(

MBF1,MBF2)oftheparallelmailboxregisterHIGH. AfteraFIFOisreset,

itsInputReadyflagissetHIGHaftertwoclockcyclestobeginnormaloperation.

A LOW-to-HIGH transition on a FIFO Reset (

RST1,RST2)inputlatchesthe

value of the Flag Select (FS0, FS1) inputs for choosing the Almost-Full and

Almost-Empty offset programming method. (For details see Table 1, Flag

Programming,andtheProgrammingtheAlmost-EmptyandAlmost-FullFlags

section). The relevant FIFO Reset timing diagram can be found in Figure 2.

FIRST WORD FALL THROUGH (

FWFT)

After Master Reset, the FWFT select function is active, permitting a choice

between two possible timing modes: IDT Standard mode or First Word Fall

Through (FWFT) mode. Once the Reset (

RST1,RST2)inputisHIGH,aHIGH

on the

FWFT input during the next LOW-to-HIGH transition of CLKA (for

FIFO1) and CLKB (for FIFO2) will select IDT Standard mode. This mode uses

the Empty Flag function (

EFA, EFB) to indicate whether or not there are any

words present in the FIFO memory. It uses the Full Flag function (

FFA, FFB)

to indicate whether or not the FIFO memory has any free space for writing. In

IDT Standard mode, every word read from the FIFO, including the first, must

be requested using a formal read operation.

Once the Reset (

RST1, RST2) input is HIGH, a LOW on the FWFT input

during the next LOW-to-HIGH transition of CLKA (for FIFO1) and CLKB (for

FIFO2) will select FWFT mode. This mode uses the Output Ready function

(ORA, ORB) to indicate whether or not there is valid data at the data outputs

(A0-A35orB0-B35). ItalsousestheInputReadyfunction(IRA,IRB)toindicate

whether or not the FIFO memory has any free space for writing. In the FWFT

mode, the first word written to an empty FIFO goes directly to data outputs, no

NOTES:

1. X1 register holds the offset for

AEB; Y1 register holds the offset for AFA.

2. X2 register holds the offset for

AEA; Y2 register holds the offset for AFB.

3. If parallel programming is selected during a Master Reset, then FS0 & FS1 must remain LOW during FIFO operation.

FS1

FS0

RST1

RST2

HH

↑

X64

X

HH

X

↑

X64

HL

↑

X16

X

HL

X

↑

X16

LH

↑

X8

X

LH

X

↑

X8

LL

↑↑

TABLE 1 — FLAG PROGRAMMING