基于AT89C52单片机的交通灯控制系统设计(外文翻译)

uto-reloadmode.ThisfeatureisinvokedbytheDCEN(DownCounterEnable)bitlocatedintheSFRT2MOD.Uponreset,theDCENbitissetto0sothattimer2willdefaulttocountup.WhenDCENisset,Timer2cancountupordown,dependingonthevalueoftheT2EXpin.Figure2showsTimer2automaticallycountingupwhenDCEN=0.Inthismode,twooptionsareselectedbybitEXEN2inT2CON.IfEXEN2=0,Timer2countsupto0FFFFHandthensetstheTF2bituponoverflow.Theoverflowalsocausesthetimerregisterstobereloadedwiththe16-bitvalueinRCAP2HandRCAP2L.ThevaluesinTimerinCaptureModeRCAP2HandRCAP2Larepresetbysoftware.IfEXEN2=1,a16-bitreloadcanbetriggeredeitherbyanoverfloworbya1-to-0transitionatexternalinputT2EX.ThistransitionalsosetstheEXF2bit.BoththeTF2andEXF2bitscangenerateaninterruptifenabled.SettingtheDCENbitenablesTimer2tocountupordown,asshowninFigure3.Inthismode,theT2EXpin