13

COMMERCIALTEMPERATURERANGE

IDT723624/723634/723644 CMOS SyncBiFIFO™ WITH BUS-MATCHING

256 x 36 x 2, 512 x 36 x 2, 1,024 x 36 x 2

Synchronized

Synchronized

Number of Words in FIFO Memory(1,2)

to CLKA

to CLKB

IDT723624(3)

IDT723634(3)

IDT723644(3)

EFA/ORA

AEA

AFB

FFB/IRB

000

L

L

H

H

1 to X2

1 to X2

1 to X2

H

L

H

H

(X2+1)to[256-(Y2+1)]

(X2+1)to[512-(Y2+1)]

(X2+1)to[1,024-(Y2+1)]

H

H

H

H

(256-Y2)to255

(512-Y2)to511

(1,024-Y2)to1,023

H

H

L

H

256

512

1,024

H

H

L

L

TABLE 4 — FIFO1 FLAG OPERATION (IDT Standard and FWFT modes)

TABLE 5 — FIFO2 FLAG OPERATION (IDT Standard and FWFT modes)

Synchronized

Synchronized

Number of Words in FIFO Memory(1,2)

to CLKB

to CLKA

IDT723624(3)

IDT723634(3)

IDT723644(3)

EFB/ORB

AEB

AFA

FFA/IRA

00

0

L

L

H

H

1 to X1

1 to X1

1 to X1

H

L

H

H

(X1+1)to[256-(Y1+1)]

(X1+1)to[512-(Y1+1)]

(X1+1)to[1,024-(Y1+1)]

H

H

H

H

(256-Y1)to255

(512-Y1)to511

(1,024-Y1)to1,023

H

H

L

H

256

512

1,024

H

H

L

L

EFB/ORB,AEB, FFB/IRB,andAFBaresynchronizedtoCLKB.Tables4and

5 show the relationship of each port flag to FIFO1 and FIFO2.

EMPTY/OUTPUT READY FLAGS (EFA/ORA, EFB/ORB)

Thesearedualpurposeflags. IntheFWFTmode,theOutputReady(ORA,

ORB) function is selected. When the Output Ready flag is HIGH, new data is

presentintheFIFOoutputregister.WhentheOutputReadyflagisLOW,the

previousdatawordispresentintheFIFOoutputregisterandattemptedFIFO

reads are ignored.

IntheIDTStandardmode,theEmptyFlag(EFA,EFB)functionisselected.

When the Empty Flag is HIGH, data is available in the FIFO’s RAM memory

for reading to the output register.WhentheEmptyFlagisLOW,theprevious

datawordispresentintheFIFOoutputregisterandattemptedFIFOreadsare

ignored.

The Empty/Output Ready flag of a FIFO is synchronized to the port clock

that reads data from its array. For both the FWFT and IDT Standard modes,

the FIFO read pointer is incremented each time a new word is clocked to its

outputregister.ThestatemachinethatcontrolsanOutputReadyflagmonitors

a write pointer and read pointer comparator that indicates when the FIFO

memorystatusisempty,empty+1,orempty+2.

In FWFT mode, from the time a word is written to a FIFO, it can be shifted

to the FIFO output register in a minimum of three cycles of the Output Ready

flagsynchronizingclock.Therefore,anOutputReadyflagisLOWifawordin

memoryisthenextdatatobesenttotheFlFOoutputregisterandthreecycles

oftheportClockthatreadsdatafromtheFIFOhavenotelapsedsincethetime

the word was written. The Output Ready flag of the FIFO remains LOW until

thethirdLOW-to-HIGHtransitionofthesynchronizingclockoccurs,simulta-

neouslyforcingtheOutputReadyflagHIGHandshiftingthewordtotheFIFO

outputregister.

InIDTStandardmode,fromthetimeawordiswrittentoaFIFO,theEmpty

Flagwillindicatethepresenceofdataavailableforreadinginaminimumoftwo

cyclesoftheEmptyFlagsynchronizingclock.Therefore,anEmptyFlagisLOW

if a word in memory is the next data to be sent to the FlFO output register and

two cycles of the port Clock that reads data from the FIFO have not elapsed

sincethetimethewordwaswritten.TheEmptyFlagoftheFIFOremainsLOW

until the second LOW-to-HIGH transition of the synchronizing clock occurs,

forcing the Empty Flag HIGH; only then can data be read.

ALOW-to-HIGHtransitiononanEmpty/OutputReadyflagsynchronizing

clockbeginsthefirstsynchronizationcycleofawriteiftheclocktransitionoccurs

NOTES:

1. When a word loaded to an empty FIFO is shifted to the output register, its previous FIFO memory location is free.

2. Data in the output register does not count as a "word in FIFO memory". Since in FWFT mode, the first word written to an empty FIFO goes unrequested to the output register

(no read operation necessary), it is not included in the FIFO memory count.

3. X1 is the Almost-Empty offset for FIFO1 used by AEB. Y1 is the Almost-Full offset for FIFO1 used by AFA. Both X1 and Y1 are selected during a FIFO1 reset or port A programming.

4. The ORB and IRA functions are active during FWFT mode; the EFB and FFA functions are active in IDT Standard mode.

NOTES:

1. When a word loaded to an empty FIFO is shifted to the output register, its previous FIFO memory location is free.

2. Data in the output register does not count as a "word in FIFO memory". Since in FWFT mode, the first word written to an empty FIFO goes unrequested to the output register

(no read operation necessary), it is not included in the FIFO memory count.

3. X2 is the Almost-Empty offset for FIFO2 used by AEA. Y2 is the Almost-Full offset for FIFO2 used by AFB. Both X2 and Y2 are selected during a FIFO2 reset or port A programming.

4. The ORA and IRB functions are active during FWFT mode; the EFA and FFB functions are active in IDT Standard mode.