HT82B42R datasheet(34/86 Pages) HOLTEK

34 / 86 page

Rev. 1.00

October 27, 2011

Rev. 1.00

October 27, 2011

HT82B42R/HT82B42RE

I/O MCU with USB Interface

Ti me r

Ex te rn al T im er

Pi n I npu t

T0 ON o r T1 ON

(w it h T0 E or T 1E =0 )

Pr es c al er O ut put

In c re me nt

Ti me r C oun te r

Pr es c al er O ut put i s sa mp le d at e ve ry fa lli ng edge o f T1 .

Pulse Width Capture Mode Timing Chart

I/O Interfacing

TheTimer/EventCounter,whenconfiguredtorunintheeventcounterorpulsewidthmeasurement

mode,requiretheuseoftheexternalTMR0andTMR1pinsforcorrectoperation.Asthesepins

aresharedpinstheymustbeconfiguredcorrectlytoensuretheyaresetupforuseasTimer/Event

CounterinputsandnotasanormalI/Opins.Thisisimplementedbyensuringthatthemodeselect

bitsintheTimer/EventCountercontrolregister,selecteithertheeventcounterorpulsewidth

measurementmode.AdditionallythePortControlRegisterbitsforthesepinsmustbesethighto

ensurethatthepinissetupasaninput.Anypull-highresistorconfigurationoptiononthesepinswill

remainvalidevenifthepinisusedasaTimer/EventCounterinput.

Programming Considerations

Whenconfiguredtoruninthetimermode,theinternalsystemclockisusedasthetimerclock

sourceandisthereforesynchronisedwiththeoveralloperationofthemicrocontroller.Inthismode

whentheappropriatetimerregisterisfull,themicrocontrollerwillgenerateaninternalinterrupt

signaldirectingtheprogramflowtotherespectiveinternalinterruptvector.Forthepulsewidth

measurementmode,theinternalsystemclockisalsousedasthetimerclocksourcebutthetimer

willonlyrunwhenthecorrectlogicconditionappearsontheexternaltimerinputpin.Asthisis

anexternaleventandnotsynchronisedwiththeinternaltimerclock,themicrocontrollerwillonly

seethisexternaleventwhenthenexttimerclockpulsearrives.Asaresult,theremaybesmall

differencesinmeasuredvaluesrequiringprogrammerstotakethisintoaccountduringprogramming.

Thesameappliesifthetimerisconfiguredtobeintheeventcountingmode,whichagainisan

externaleventandnotsynchronisedwiththeinternalsystemortimerclock.

WhentheTimer/EventCounterisread,orifdataiswrittentothepreloadregister,theclockis

inhibitedtoavoiderrors,howeverasthismayresultinacountingerror,thisshouldbetakeninto

accountbytheprogrammer.Caremustbetakentoensurethatthetimersareproperlyinitialised

beforeusingthemforthefirsttime.Theassociatedtimerenablebitsintheinterruptcontrol

registermustbeproperlysetotherwisetheinternalinterruptassociatedwiththetimerwillremain

inactive.Theedgeselecttimermodeandclocksourcecontrolbitsintimercontrolregistermust

alsobecorrectlysettoensurethetimerisproperlyconfiguredfortherequiredapplication.Itis

alsoimportanttoensurethataninitialvalueisfirstloadedintothetimerregistersbeforethetimer

isswitchedon;thisisbecauseafterpower-ontheinitialvaluesofthetimerregistersareunknown.

Afterthetimerhasbeeninitialisedthetimercanbeturnedonandoffbycontrollingtheenablebitin

thetimercontrolregister.Notethatsettingthetimerenablebithightoturnthetimeron,shouldonly

beexecutedafterthetimermodebitshavebeenproperlysetup.Settingthetimerenablebithigh

togetherwithamodebitmodification,mayleadtoimpropertimeroperationifexecutedasasingle

timercontrolregisterbytewriteinstruction.

HT82B42R Datasheet(PDF) 34 Page - Holtek Semiconductor Inc

HT82B42R Datasheet(HTML) 34 Page - Holtek Semiconductor Inc

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