IDT72421/72201/72211/72221/72231/72241/72251 CMOS SyncFIFO™
64 x 9, 256 x 9, 512 x 9, 1,024 x 9, 2,048 x 9, 4,096 x 9 and 8,192 x 9
COMMERCIALANDINDUSTRIAL
TEMPERATURERANGES
configuration,theWriteEnable2/Load(WEN2/LD)pinissetLOWatResetso
thatthepinoperatesasacontroltoloadandreadtheprogrammableflagoffsets.
OPERATINGCONFIGURATIONS
SINGLE DEVICE CONFIGURATION
AsingleIDT72421/72201/72211/72221/72231/72241/72251maybeused
when the application requirements are for 64/256/512/1,024/2,048/4,096/
8,192wordsorless.WhentheseFIFOsareinaSingleDeviceConfiguration,
theReadEnable2(REN2)controlinputcanbegrounded(seeFigure14). In
thisconfiguration,theWriteEnable2/Load(WEN2/LD)pinissetLOWatReset
sothatthe pinoperates as a controltoloadandreadthe programmable flag
offsets.
DEPTH EXPANSION - The IDT72421/72201/72211/72221/72231/72241/
72251canbeadaptedtoapplicationswhentherequirementsareforgreater
than 64/256/512/1,024/2,048/4,096/8,192 words. The existence of two
enable pins on the read and write port allow depth expansion. The Write
Enable 2/Load pin is used as a second write enable in a depth expansion
configurationthustheProgrammableflagsaresettothedefaultvalues. Depth
expansionis possiblebyusingoneenableinputforsystemcontrolwhilethe
otherenableinputiscontrolledbyexpansionlogictodirecttheflowofdata. A
typicalapplicationwouldhavetheexpansionlogicalternatedataaccessfrom
onedevicetothenextinasequentialmanner. Thesedevices operateinthe
DepthExpansionconfigurationwhenthefollowingconditionsaremet:
1. The WEN2/ LD pin is held HIGH during Reset so that this pin operates a
secondWriteEnable.
WIDTH EXPANSION CONFIGURATION
Wordwidthmaybeincreasedsimplybyconnectingthecorrespondinginput
controlssignalsofmultipledevices. Acompositeflagshouldbecreatedforeach
oftheendpointstatusflags(EFandFF). Thepartialstatusflags(AEandAF)
canbedetectedfromanyonedevice. Figure15demonstratesa18-bitword
width by using two IDT72421/72201/72211/72221/72231/72241/72251s.
AnywordwidthcanbeattainedbyaddingadditionalIDT72421/72201/72211/
72221/72231/72241/72251s.
2. Externallogicis usedtocontrolthe flowofdata.
Please see the Application Note "DEPTH EXPANSION OF IDT'S SYN-
CHRONOUSFIFOsUSINGTHERINGCOUNTERAPPROACH"fordetails
ofthisconfiguration.
When these FIFOs are in a Width Expansion Configuration, the Read
Enable 2 (REN2) control input can be grounded (see Figure 15). In this
RESET (RS)
WRITE CLOCK (WCLK)
WRITE ENABLE 1 (WEN1)
READ CLOCK (RCLK)
IDT
READ ENABLE 1 (REN1)
OUTPUT ENABLE (OE)
72421
72201
72211
72221
72231
72241
72251
WRITE ENABLE 2/LOAD (WEN2/LD)
DATA IN (D
0
- D8)
DATA OUT (Q
EMPTY FLAG (EF)
PROGRAMMABLE ALMOST-EMPTY (PAE)
0 - Q8)
FULL FLAG (FF)
PROGRAMMABLE ALMOST-FULL (PAF)
2655 drw 16
READ ENABLE 2 (REN2)
Figure 14. Block Diagram of Single 64 x 9, 256 x 9, 512 x 9, 1,024 x 9, 2,048 x 9, 4,096 x 9, 8,192 x 9 Synchronous FIFO
RESET (RS)
RESET (RS)
DATA IN (D)
18
9
9
READ CLOCK (RCLK)
WRITE CLOCK (WCLK)
READ ENABLE (REN)
OUTPUT ENABLE (OE)
PROGRAMMABLE (PAE)
WRITE ENABLE1 (WEN1)
IDT
IDT
72421
72201
72211
72221
72231
72241
72251
72421
72201
72211
72221
72231
72241
72251
WRITE ENABLE2/LOAD (WEN2/LD)
FULL FLAG (FF) #1
FULL FLAG (FF) #2
EMPTY FLAG (EF) #1
EMPTY FLAG (EF) #2
9
PROGRAMMABLE (PAF)
18
9
DATA OUT (Q)
2655 drw 17
READ ENABLE 2 (REN2)
READ ENABLE 2 (REN2)
Figure 15. Block Diagram of 64 x 18, 256 x 18, 512 x 18, 1,024 x 18, 2,048 x 18, 4,096 x 18, 8,192 x 18
Synchronous FIFO Used in a Width Expansion Configuration
©
OCTOBER22,2008
13
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