6

256 x 18, 512 x 18, 1,024 x 18, 2,048 x 18 and 4,096 x 18

COMMERCIALANDINDUSTRIAL

TEMPERATURERANGES

FUNCTIONAL DESCRIPTION

TIMING MODES: IDT STANDARD vs FIRST WORD FALL THROUGH

(FWFT) MODE

The IDT72V205/72V215/72V225/72V235/72V245 support two different

timing modes of operation. The selection of which mode will operate is

determinedduringconfigurationatReset(

RS).Duringa RSoperation,theFirst

Load(

FL),ReadExpansionInput(RXI),andWriteExpansionInput(WXI)pins

are used to select the timing mode per the truth table shown in Table 3. In IDT

Standard Mode, the first word written to an empty FIFO will not appear on the

dataoutputlinesunlessaspecificreadoperationisperformed.Areadoperation,

which consists of activating Read Enable (

REN) and enabling a rising Read

Clock (RCLK) edge, will shift the word from internal memory to the data output

lines. In FWFT mode, the first word written to an empty FIFO is clocked directly

to the data output lines after three transitions of the RCLK signal. A

RENdoes

not have to be asserted for accessing the first word.

Varioussignals,bothinputandoutputsignalsoperatedifferentlydepending

on which timing mode is in effect.

IDT STANDARD MODE

In this mode, the status flags,

FF, PAF, HF, PAE, and EF operate in the

manner outlined in Table 1. To write data into to the FIFO, Write Enable (

WEN)

mustbeLOW.DatapresentedtotheDATAINlineswillbeclockedintotheFIFO

on subsequent transitions of the Write Clock (WCLK). After the first write is

performed, the Empty Flag (

EF)willgoHIGH.Subsequentwriteswillcontinue

to fill up the FIFO. The Programmable Almost-Empty flag (

PAE)willgoHIGH

after n + 1 words have been loaded into the FIFO, where n is the empty offset

value. The default setting for this value is stated in the footnote of Table 1. This

parameter is also user programmable. See section on Programmable Flag

OffsetLoading.

If one continued to write data into the FIFO, and we assumed no read

operationsweretakingplace,theHalf-FullFlag(

HF)wouldtoggletoLOWonce

the 129th (72V205), 257th (72V215), 513th (72V225), 1,025th (72V235), and

2,049th (72V245) word respectively was written into the FIFO. Continuing to

write data into the FIFO will cause the Programmable Almost-Full Flag (

PAF)

togoLOW.Again,ifnoreadsareperformed, the

PAFwillgoLOWafter(256-m)

writes for the IDT72V205, (512-m) writes for the IDT72V215, (1,024-m) writes

for the IDT72V225, (2,048-m) writes for the IDT72V235 and (4,096–m) writes

fortheIDT72V245. Theoffset“m”isthefulloffsetvalue. Thisparameterisalso

userprogrammable.SeesectiononProgrammableFlagOffsetLoading. Ifthere

is no full offset specified, the

PAFwillbeLOWwhenthedeviceis31awayfrom

completelyfullforIDT72V205,63awayfromcompletelyfullforIDT72V215,and

127 away from completely full for the IDT72V225/72V235/72V245.

When the FIFO is full, the Full Flag (

FF)willgoLOW,inhibitingfurtherwrite

operations. Ifnoreadsareperformedafterareset,

FFwillgoLOWafterDwrites

to the FIFO. D = 256 writes for the IDT72V205, 512 for the IDT72V215, 1,024

for the IDT72V225, 2,048 for the IDT72V235 and 4,096 for the IDT72V245,

respectively.

If the FIFO is full, the first read operation will cause

FF to go HIGH.

Subsequent read operations will cause

PAFand the Half-Full Flag (HF) to go

HIGH at the conditions described in Table 1. If further read operations occur,

without write operations, the Programmable Almost-Empty Flag (

PAE)willgo

LOW when there are n words in the FIFO, where n is the empty offset value.

If there is no empty offset specified, the

PAEwillbeLOWwhenthedeviceis31

away from completely empty for IDT72V205, 63 away from completely empty

forIDT72V215,and127awayfromcompletelyemptyforIDT72V225/72V235/

72V245. Continuing read operations will cause the FIFO to be empty. When

thelastwordhasbeenreadfromtheFIFO,the

EFwillgoLOWinhibitingfurther

read operations.

REN is ignored when the FIFO is empty.

FIRST WORD FALL THROUGH MODE (FWFT)

In this mode, the status flags,

IR, PAF, HF, PAE, and OR operate in the

manner outlined in Table 2. To write data into to the FIFO,

WENmustbeLOW.

DatapresentedtotheDATAINlineswillbeclockedintotheFIFOonsubsequent

transitions of WCLK. After the first write is performed, the Output Ready (

OR)

flag will go LOW. Subsequent writes will continue to fill up the FIFO.

PAEwillgo

HIGH after n + 2 words have been loaded into the FIFO, where n is the empty

offsetvalue.ThedefaultsettingforthisvalueisstatedinthefootnoteofTable2.

Thisparameterisalsouserprogrammable.SeesectiononProgrammableFlag

OffsetLoading.

If one continued to write data into the FIFO, and we assumed no read

operations were taking place, the

HF would toggle to LOW once the 130th

(72V205), 258th (72V215), 514th (72V225), 1,026th (72V235), and 2,050th

(72V245) word respectively was written into the FIFO. Continuing to write data

into the FIFO will cause the

PAFtogoLOW.Again,ifnoreadsareperformed,

the

PAF will go LOW after (257-m) writes for the IDT72V205, (513-m) writes

for the IDT72V215, (1,025-m) writes for the IDT72V225, (2,049–m) writes for

the IDT72V235 and (4,097–m) writes for the IDT72V245, where m is the full

offset value. The default setting for this value is stated in the footnote of Table

2.

WhentheFIFOisfull,theInputReady(

IR)flagwillgoHIGH,inhibitingfurther

write operations. If no reads are performed after a reset,

IRwillgoHIGHafter

DwritestotheFIFO. D=257writesfortheIDT72V205,513fortheIDT72V215,

1,025 for the IDT72V225, 2,049 for the IDT72V235 and 4,097 for the

IDT72V245. Note that the additional word in FWFT mode is due to the capacity

of the memory plus output register.

If the FIFO is full, the first read operation will cause the

IR flag to go LOW.

Subsequent read operations will cause the

PAF and HF to go HIGH at the

conditions described in Table 2. If further read operations occur, without write

operations,the

PAEwillgoLOWwhentherearen+1wordsintheFIFO,where

n is the empty offset value. If there is no empty offset specified, the

PAEwillbe

LOW when the device is 32 away from completely empty for IDT72V205, 64

away from completely empty for IDT72V215, and 128 away from completely

emptyforIDT72V225/72V235/72V245.Continuingreadoperationswillcause

the FIFO to be empty. When the last word has been read from the FIFO,

OR

will go HIGH inhibiting further read operations.

RENisignoredwhentheFIFO

isempty.

PROGRAMMABLE FLAG LOADING

FullandEmptyflagoffsetvaluescanbeuserprogrammable.TheIDT72V205/

72V215/72V225/72V235/72V245 has internal registers for these offsets.

DefaultsettingsarestatedinthefootnotesofTable1andTable2.Offsetvalues

registers, the Load (

LD)pinandWENpinmustbeheldLOW.Datapresenton

transitionofWCLK.Bycontinuingtoholdthe

LDandWENpinlow, datapresent

oftheWCLK.ThethirdtransitionagainwritestotheEmptyOffsetregister. Writing

alloffsetregistersdoesnothavetooccuratonetime.Oneortwooffsetregisters

can be written and then by bringing the

LD pin HIGH, the FIFO is returned to

normal read/write operation. When the

LD pin and WEN are again set LOW,

the next offset register in sequence is written.