Texas Instruments TMS320x28xx Network Router User Manual


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UP
DOWN
UP
DOWN
2
0
3
4
1
2
3
1
2
0
3
4
1
2
0
3
1
TBCNTR
TBCNTRDirection
EPWMxA/EPWMxB
Case2:
CMPA =3,25%Duty
Case3:
CMPA =2,50%Duty
Case3:
CMPA =1,75%Duty
Case4:
CMPA =0,100%Duty
Case1:
CMPA =4,0%Duty
EPWMxA/EPWMxB
EPWMxA/EPWMxB
EPWMxA/EPWMxB
EPWMxA/EPWMxB
Mode:Up-DownCount
TBPRD=4
CAU=SET,CAD=CLEAR
0%-100%Duty
Action-Qualifier(AQ)Submodule
Whenusingthisconfigurationinpractice,ifyouloadCMPA/CMPBonzero,thenuseCMPA/CMPBvalues
greaterthanorequalto1.IfyouloadCMPA/CMPBonperiod,thenuseCMPA/CMPBvalueslessthanor
equaltoTBPRD-1.ThismeanstherewillalwaysbeapulseofatleastoneTBCLKcycleinaPWMperiod
which,whenveryshort,tendtobeignoredbythesystem.
Figure2-20.Up-Down-CountModeSymmetricalWaveform
ThePWMwaveformsinFigure2-21throughFigure2-26showsomecommonaction-qualifier
configurations.TheC-codesamplesinExample2-2throughExample2-7showshowtoconfigurean
ePWMmoduleforeachcase.Someconventionsusedinthefiguresandexamplesareasfollows:
•TBPRD,CMPA,andCMPBrefertothevaluewrittenintheirrespectiveregisters.Theactiveregister,
nottheshadowregister,isusedbythehardware.
•CMPx,referstoeitherCMPAorCMPB.
•EPWMxAandEPWMxBrefertotheoutputsignalsfromePWMx
•Up-DownmeansCount-up-and-downmode,Upmeansup-countmodeandDwnmeansdown-count
mode
•Sym=Symmetric,Asym=Asymmetric
42ePWMSubmodulesSPRU791D–November2004–RevisedOctober2007
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