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5.2.2.2ChangingPLLMultiplier
PLL1Control
IfthePLLisnotpowereddown(PLLPWRDNbitinPLLCTLisclearedto0)andthePLLstabilizationtime
ispreviouslymet(step7inSection5.2.2.1),followthisproceduretochangePLL1multiplier.The
recommendationistostopallperipheraloperationbeforechangingthePLLmultiplier,withtheexception
oftheC64x+DSPandDDR2.TheC64x+DSPmustbeoperationaltoprogramthePLLcontroller.DDR2
operatesoffoftheclockfromPLLC2.
1.BeforechangingthePLLfrequency,switchtoPLLbypassmode:
a.ClearthePLLENSRCbitinPLLCTLto0toallowPLLCTL.PLLENtotakeeffect.
b.ClearthePLLENbitinPLLCTLto0(selectPLLbypassmode).
c.Waitfor4MXIcyclestoensurePLLCswitchestobypassmodeproperly.
2.ClearthePLLRSTbitinPLLCTLto0(resetPLL).
3.ClearthePLLDISbitinPLLCTLto0(enablethePLL)toallowPLLoutputstostarttoggling.Notethat
thePLLCisstillatPLLbypassmode;therefore,thetogglingPLLoutputdoesnotgetpropagatedto
therestofthedevice.
4.ProgramtherequiredmultipliervalueinPLLM.
5.Ifnecessary,programPLLDIV1,PLLDIV2,andPLLDIV3registerstochangetheSYSCLK1,SYSCLK2,
andSYSCLK3dividevalues:
a.CheckfortheGOSTATbitinPLLSTATtoclearto0toindicatethatnoGOoperationiscurrentlyin
progress.
b.ProgramtheRATIOfieldinPLLDIV1,PLLDIV2,andPLLDIV3withthedesireddividefactors.Note
thatthedividersmustmaintaina1:3:6ratiotosatisfytheCLKDIV1,CLKDIV3,CLKDIV6clock
domainrequirements.Seethedevice-specificdatamanualformoredetailsonClockDomains.In
addition,makesureinthisstepyouleavethePLLDIV1.D1EN,PLLDIV2.D2EN,and
PLLDIV3.D3ENbitsset(default).
c.SettheGOSETbitinPLLCMDto1toinitiateanewdividertransition.Duringthistransition,
SYSCLK1,SYSCLK2,andSYSCLK3arepausedmomentarily.
d.WaitforNnumberofPLLDIVnsourceclockcyclestoensuredividerchangeshavecompleted.See
Section5.2.2.3fortheformulaoncalculatingthenumberofcyclesN.
e.WaitfortheGOSTATbitinPLLSTATtoclearto0.
6.WaitforPLLtoresetproperly.Seethedevice-specificdatamanualforPLLresettime.
7.SetthePLLRSTbitinPLLCTLto1tobringthePLLoutofreset.
8.WaitforPLLtolock.Seethedevice-specificdatamanualforPLLlocktime.
9.SetthePLLENbitinPLLCTLto1toremovethePLLfrombypassmode.
SPRU978E–March2008PLLController41
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