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2PeripheralArchitecture
2.1ClockControl
2.1.1ClockSource
DDR2
memory
controller
/2
PLLC2
/3
PLLC1
X2_CLKVCLK
DDR_CLK
DDR_CLK
PLL2_SYSCLK1
SYSCLK2
PeripheralArchitecture
ThissectiondescribesthearchitectureoftheDDR2memorycontrolleraswellashowitisstructuredand
howitworkswithinthecontextofthesystem-on-a-chip.TheDDR2memorycontrollercangluelessly
interfacetomoststandardDDR2SDRAMdevicesandsupportssuchfeaturesasself-refreshmodeand
prioritizedrefresh.Inaddition,itprovidesflexibilitythroughprogrammableparameterssuchastherefresh
rate,CASlatency,andmanySDRAMtimingparameters.Thefollowingsectionsincludedetailsonhowto
interfaceandproperlyconfiguretheDDR2memorycontrollertoperformreadandwriteoperationsto
externally-connectedDDR2SDRAMdevices.Also,Section3providesadetailedexampleofinterfacing
theDDR2memorycontrollertoacommonDDR2SDRAMdevice.
TheDDR2memorycontrollerreceivestwoinputclocksfrominternalclocksources,SYSCLK2and
PLL2_SYSCLK1(Figure2).SYSCLK2isadivided-downversionoftheDSPclock.PLL2_SYSCLK1
shouldbeconfiguredtoclockatthefrequencyofthedesireddatarate,orstatedsimilarly,itshould
operateattwicethefrequencyofthedesiredDDR2memoryclock.DDR_CLKandDDR_CLKarethetwo
outputclocksoftheDDR2memorycontrollerprovidingtheinterfaceclocktotheDDR2SDRAMmemory.
ThesetwoclocksoperateatafrequencyofPLL2_SYSCLK1/2.
SYSCLK2andPLL2_SYSCLK1aresourcedfromtwoindependentPLLs(Figure2).SYSCLK2issourced
fromPLLcontroller1(PLLC1)andPLL2_SYSCLK1issourcedfromPLLcontroller2(PLLC2).
SYSCLK2isclockedatafixeddividerratioofPLL1.Thisdividerisfixedat3,meaningSYSCLK2is
clockedatafrequencyofPLL1/3.OnceinsidetheDDR2memorycontroller,thissignaliscalledVCLK.
PLLC2hasaprogrammabledividerthatisusedtodivide-downtheoutputclockofPLL2.Thisdivider
shouldbeconfiguredsuchthatPLLC2suppliesthePLL2_SYSCLK1atthedesiredfrequency.For
example,ifa150-MHZDDR2interfaceclock(DDR_CLK)isdesired,thenPLLC2mustbeconfiguredto
generatea300-MHZclockonPLL2_SYSCLK1.OnceinsidetheDDR2memorycontroller,
PLL2_SYSCLK1iscalledX2_CLK.
Figure2.DDR2MemoryControllerClockBlockDiagram
SPRU986B–November2007DDR2MemoryController9
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