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IDT72V285L10TFI Datasheet(PDF) 7 Page - Integrated Device Technology |
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IDT72V285L10TFI Datasheet(HTML) 7 Page - Integrated Device Technology |
7 / 25 page 7 COMMERCIALANDINDUSTRIALTEMPERATURERANGE IDT72V275/72V285 WhenconfiguredinIDTStandardmode,the EFandFFoutputsaredouble register-bufferedoutputs. Relevant timing diagrams for IDT Standard mode can be found in Figure 7, 8 and 11. FIRST WORD FALL THROUGH MODE (FWFT) In this mode, the status flags, IR,PAF,HF,PAE,andORoperateinthe manneroutlinedinTable2.TowritedataintototheFIFO, 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. PAEwill goHIGHaftern + 2wordshavebeenloadedintotheFIFO,wherenistheempty offsetvalue.ThedefaultsettingforthisvalueisstatedinthefootnoteofTable2. Thisparameterisalsouserprogrammable.SeesectiononProgrammableFlag OffsetLoading. If one continued to write data into the FIFO, and we assumed no read operations were taking place, the HFwouldtoggletoLOWoncethe16,386th word for the IDT72V275 and 32,770th word for the IDT72V285, respectively was written into the FIFO. Continuing to write data into the FIFO will cause the PAFtogoLOW.Again,ifnoreadsareperformed, thePAFwillgoLOWafter (32,769-m)writesfortheIDT72V275 and(65,537-m)writesfortheIDT72V285, 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 D writes to the FIFO. D = 32,769 writes for the IDT72V275 and 65,537 writes for the IDT72V285, respectively. 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 IRflag 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. Continuing read operations will cause the FIFO to become empty. When the last word has been read from the FIFO, ORwillgo HIGH inhibiting further read operations. REN is ignored when the FIFO is empty. When configured in FWFT mode, the OR flag output is triple register- buffered, and the IR flagoutputisdoubleregister-buffered. Relevant timing diagrams for FWFT mode can be found in Figure 9, 10 and 12. PROGRAMMING FLAG OFFSETS FullandEmptyFlagoffsetvaluesareuserprogrammable.TheIDT72V275/ 72V285hasinternalregistersfortheseoffsets.Defaultsettingsarestatedinthe footnotesofTable1andTable2.OffsetvaluescanbeprogrammedintotheFIFO inoneoftwoways;serialorparallelloadingmethod.Theselectionoftheloading method is done using the LD(Load)pin.DuringMasterReset,thestateofthe LD input determines whether serial or parallel flag offset programming is enabled. A HIGH on LD during Master Reset selects serial loading of offset values and in addition, sets a default PAE offset value of 3FFH (a threshold 1,023wordsfromtheemptyboundary),andadefault PAFoffsetvalueof3FFH (a threshold 1,023 words from the full boundary). A LOW on LDduringMaster Resetselectsparallelloadingofoffsetvalues,andinaddition,setsadefault PAE offset value of 07FH (a threshold 127 words from the empty boundary), and a default PAF offset value of 07FH (a threshold 127 words from the full boundary). See Figure 3, Offset Register Location and Default Values. In addition to loading offset values into the FIFO, it also possible to read the current offset values. It is only possible to read offset values via parallel read. .UNCTIONAL DESCRIPTION TIMING MODES: IDT STANDARD vs FIRST WORD FALL THROUGH (FWFT) MODE The IDT72V275/72V285 support two different timing modes of operation: IDT Standard mode or First Word Fall Through (FWFT) mode. The selection of which mode will operate is determined during Master Reset, by the state of the FWFT/SI input. If, at the time of Master Reset, FWFT/SI is LOW, then IDT Standard mode will be selected. This mode uses the Empty Flag ( EF) to indicate whether or not there are any words present in the FIFO. It also uses the Full Flag function ( FF)toindicatewhetherornottheFIFOhasanyfreespaceforwriting. InIDT Standard mode, every word read from the FIFO, including the first, must be requested using the Read Enable ( REN) and RCLK. If, at the time of Master Reset, FWFT/SI is HIGH, then FWFT mode will be selected. This mode uses Output Ready ( OR)toindicatewhetherornotthere is valid data at the data outputs (Qn). It also uses Input Ready ( IR)toindicate whether or not the FIFO has any free space for writing. In the FWFT mode, thefirstwordwrittentoanemptyFIFOgoesdirectlytoQnafterthreeRCLKrising edges, REN=LOWisnotnecessary. Subsequentwordsmustbeaccessed using the Read Enable ( REN) and RCLK. Varioussignals,bothinputandoutputsignalsoperatedifferentlydepending on which timing mode is in effect. IDT STANDARD MODE In this mode, the status flags, FF,PAF,HF,PAE,andEFoperateinthe manneroutlinedinTable1.TowritedataintototheFIFO,WriteEnable( 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 16,385th word for IDT72V275 and 32,769th word for IDT72V285 respectively was written into the FIFO. Continuing to write data into the FIFO will cause the Programmable Almost-Full flag ( PAF) to go LOW. Again, if no reads are performed, the PAF will go LOW after (32,768-m) writes for the IDT72V275 and (65,536-m) writes for the IDT72V285. The offset “m” is the full offsetvalue.ThedefaultsettingforthisvalueisstatedinthefootnoteofTable1. Thisparameterisalsouserprogrammable.SeesectiononProgrammableFlag OffsetLoading. When the FIFO is full, the Full Flag ( FF)willgoLOW,inhibitingfurtherwrite operations. Ifnoreadsareperformedafterareset, FFwillgoLOWafterDwrites to the FIFO. D = 32,768 writes for the IDT72V275 and 65,536 for the IDT72V285, respectively. If the FIFO is full, the first read operation will cause FF to go HIGH. Subsequent read operations will cause PAF and HF to go HIGH at the conditions described in Table 1. If further read operations occur, without write operations, PAE will go LOW when there are n words in the FIFO, where n is the empty offset value. Continuing read operations will cause the FIFO to become empty. When the last word has been read from the FIFO, the EFwill go LOW inhibiting further read operations. REN is ignored when the FIFO is empty. |
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