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IDT72V235L20PFI Datasheet(PDF) 6 Page - Integrated Device Technology |
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IDT72V235L20PFI Datasheet(HTML) 6 Page - Integrated Device Technology |
6 / 25 page 6 IDT72V205/72V215/72V225/72V235/72V245 3.3V CMOS SyncFIFOTM 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 are loaded into the FIFO using the data input lines D0-D11. To load the offset registers, the Load ( LD)pinandWENpinmustbeheldLOW.Datapresenton D0-D11willbetransferredintotheEmptyOffsetregisteronthefirstLOW-to-HIGH transitionofWCLK.Bycontinuingtoholdthe LDandWENpinlow, datapresent on D0-D11 will be transferred into the Full Offset register on the next transition 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. |
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