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IDT72T51236 Datasheet(PDF) 29 Page - Integrated Device Technology |
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IDT72T51236 Datasheet(HTML) 29 Page - Integrated Device Technology |
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29 / 62 page  29 IDT72T51236/72T51246/72T51256 2.5V, MULTI-QUEUE FLOW-CONTROL DEVICES (4 QUEUES) 36 BIT WIDE CONFIGURATION 589,824, 1,179,648 and 2,359,296 bits COMMERCIALANDINDUSTRIAL TEMPERATURERANGES PAFn BUS EXPANSION - DIRECT MODE If FM is LOW at Master Reset then the PAFn bus operates in Direct (addressed)mode.Indirectmodetheusercanaddressthedevicetheyrequire to control the PAFn bus. The address present on the 3 most significant bits of the WRADD[4:0] address bus with FSTR ( PAF flag strobe), HIGH will be selected as the device on a rising edge of WCLK. So to address the first device in a bank of devices the WRADD[4:0] address should be “000xx” the second device“001xx”andsoon.The3mostsignificantbitsoftheWRADD[4:0]address buscorrespondtothedeviceIDinputsID[2:0].The PAFnbuswillchangestatus toshowthenewdeviceselected1WCLKcycleafterdeviceselection.Note,that if a read or write operation is occurring to a specific queue, say queue ‘x’ on the same cycle as a PAFn bus switch to the device containing queue ‘x’, then there may be an extra WCLK cycle delay before that queues status is correctly shown on the respective output of the PAFn bus. However, the “active” PAF flag will show correct status at all times. Devices can be selected on consecutive WCLK cycles, that is the device controlling the PAFn bus can change every WCLK cycle. Also, data present ontheinputbus,Din,canbewrittenintoaqueueonthesameWLCKrisingedge that a device is being selected on the PAFnbus,theonlyrestrictionbeingthat awritequeueselectionand PAFnbusselectioncannotbemadeonthesamecycle. PAFn – POLLED BUS IfFMisHIGHatMasterResetthenthe PAFnbusoperatesinPolled(Looped) mode. In polled mode the PAFnbusautomaticallycyclesthroughthedevices connected in expansion. In expansion mode one device will be set as the Master,MASTinputtiedHIGH,allotherdeviceswillhaveMASTtiedLOW.The master device is the first device to take control of the PAFn bus and place the PAFstatusofitsqueuesontothebusonthefirstrisingedgeofWCLKafterthe MRSinputgoesHIGHonceaMasterResetiscomplete.TheFSYNC(PAFsync pulse) output of the first device (master device), will be HIGH for one cycle of WCLK indicating that it is has control of the PAFn bus for that cycle. The device also passes a “token” onto the next device in the chain, the next device assuming control of the PAFnbusonthenextWCLKcycle.Thistoken passing is done via the FXO outputs and FXI inputs of the devices (“ PAFn Expansion Out” and “ PAFnExpansionIn”).TheFXOoutputofthefirstdevice connecting to the FXI input of the second device in the chain, the FXO of the second device connects to the FXI of the third device and so on. The FXO of thefinaldeviceinachainconnectstotheFXIofthefirstdevice,sothatoncethe PAFn bus has cycled through all devices control is again passed to the first device.TheFXOoutputofadevicewillbeHIGHfortheWCLKcycleithascontrol of the bus. Please refer to Figure 30, PAFn Bus – Polled Mode for timing information. PAEn/PRn FLAG BUS OPERATION The IDT72T51236/72T51246/72T51256 multi-queue flow-control devices canbeconfiguredforupto4queues,eachqueuehavingitsownalmostempty/ packetreadystatus.Anactivequeuehasitsflagstatusoutputtothediscreteflags, OV, PAE and PR, on the read port. Queues that are not selected for a read operationcanhavetheir PAE/PRstatusmonitoredviathePAEn/PRnbus.The PAEn/PRnflagbusis4bitswide,sothatall4queuescanhavetheirstatusoutput to the bus. The multi-queue device can provide either “Almost Empty” status or “PacketReady”statusviathe PAEn/PRnbusofitsqueues,dependingonwhich has been selected via the PKT (Packet) input during a master reset. If PKT is HIGHthenpacketmodeisselectedandthe PAEn/PRnbuswillprovide“Packet Ready” status. If it is LOW then the PAEn/PRnbuswillprovide“AlmostEmpty” status. In either case the operation of the bus is the same the difference being that the bus is providing “Packet Ready” status versus “Almost Empty” status. Whenasinglemulti-queuedeviceisusedanywherefrom1to4queuesmay be set-up within the part, each queue having its own dedicated PAEn/PRnflag output on the PAEn/PRn bus. Queues 1 through 4 have their PAE/PRstatus to PAE[0]throughPAE[3]respectively.Iflessthan4queuesareusedthenonly theassociated PAEn/PRnoutputswillberequired,unusedPAEn/PRn outputs will be don’t care outputs. When devices are connected in expansion mode the PAEn/PRn flag bus can also be expanded beyond 4 bits to produce a wider PAEn/PRnbusthatencompassesallqueues. Alternatively, the 4 bit PAEn/PRn flagbusofeachdevicecanbeconnected together to form a single 4 bit bus, i.e. PAE[0]ofdevice1willconnecttoPAE[0] ofdevice2etc.Whenconnectingdevicesinthismannerthe PAEn/PRnbuscan onlybedrivenbyasingledeviceatanytime,(the PAEn/PRn outputsofallother devicesmustbeinhighimpedancestate).Therearetwomethodsbywhichthe user can select which device has control of the bus, these are “Direct” (Addressed) mode or “Polled” (Looped) mode, determined by the state of the FM (flag Mode) input during a Master Reset. PAEn/PRn - DIRECT BUS If FM is LOW at Master Reset then the PAEn/PRn bus operates in Direct (addressed)mode.Indirectmodetheusercanaddressthedevicetheyrequire tocontrolthe PAEn/PRnbus.Theaddresspresentonthe3mostsignificantbits of the RDADD[4:0] address bus with ESTR ( PAE/PR flag strobe), HIGH will beselectedasthedeviceonarisingedgeofRCLK.Sotoaddressthefirstdevice in a bank of devices the RDADD[4:0] address should be “000xx” the second device“001xx”andsoon.The3mostsignificantbitsoftheRDADD[5:0]address bus correspond to the device ID inputs ID[2:0]. The PAEn/PRnbuswillchange status to show the new device selected 1 RCLK cycle after device selection. Note,thatifareadorwriteoperationisoccurringtoaspecificqueue,sayqueue ‘x’onthesamecycleasa PAEn/PRnbusswitchtothedevicecontainingqueue ‘x’, then there may be an extra RCLK cycle delay before that queues status is correctly shown on the respective output of the PAEn/PRnbus.However,the “active” PAE and/or PRflag will show correct status at all times. Devices can be selected on consecutive RCLK cycles, that is the device controlling the PAEn/PRn bus can change every RCLK cycle. Also, data can be read out of a queue on the same RCLK rising edge that a device is being selected on the PAEn/PRn bus, the only restriction being that a read queue selection and PAEn/PRn bus selection cannot be made on the same cycle. PAEn/PRn- POLLED BUS If FM is HIGH at Master Reset then the PAEn/PRn bus operates in Polled (Looped)mode.Inpolledmodethe PAEn/PRnbusautomaticallycyclesthrough the devices connected in expansion. In expansion mode one device will be set astheMaster,MASTinputtiedHIGH,allotherdeviceswillhaveMASTtiedLOW. The master device is the first device to take control of the PAEn/PRn bus and placethe PAE/PRstatusofitsqueuesontothebusonthefirstrisingedgeofRCLK after the MRSinputgoesHIGHonceaMasterResetiscomplete.TheESYNC ( PAE/PRsyncpulse)outputofthefirstdevice(masterdevice),willbeHIGHfor one cycle of RCLK indicating that it is has control of the PAEn/PRnbusforthat cycle. The device also passes a “token” onto the next device in the chain, the next device assuming control of the PAEn/PRn bus on the next RCLK cycle. This tokenpassingisdoneviatheEXOoutputsandEXIinputsofthedevices(“ PAEn/ PRn Expansion Out” and “PAEn/PRn Expansion In”). The EXO output of the firstdeviceconnectingtotheEXIinputoftheseconddeviceinthechain,theEXO oftheseconddeviceconnectstotheEXIofthethirddeviceandsoon.TheEXO of the final device in a chain connects to the EXI of the first device, so that once the PAEn/PRn bus has cycled through all devices control is again passed to the first device. The EXO output of a device will be HIGH for the RCLK cycle it has control of the bus. Please refer to Figure 31, PAEn/PRn Bus – Polled Mode for timing information. |
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