HT82B42R datasheet(38/86 Pages) HOLTEK

38 / 86 page

Rev. 1.00

October 27, 2011

Rev. 1.00

October 27, 2011

HT82B42R/HT82B42RE

I/O MCU with USB Interface

Interrupt Priority

Interrupts,occurringintheintervalbetweentherisingedgesoftwoconsecutiveT2pulses,willbe

servicedonthelatterofthetwoT2pulses,ifthecorrespondinginterruptsareenabled.Incaseof

simultaneousrequests,thefollowingtableshowstheprioritythatisapplied.Thesecanbemasked

byresettingtheEMIbit.

Interrupt Source

Priority

Vector

USB Interrupt

0004H

Timer/Event Counter 0 Overflow Interrupt

0008H

Timer/Event Counter 1 Overflow Interrupt

000CH

SPI Interrupt

0010H

Incaseswherebothexternalandinternalinterruptsareenabledandwhereanexternalandinternal

interruptoccurssimultaneously,theexternalinterruptwillalwayshavepriorityandwillthereforebe

servicedfirst.Suitablemaskingoftheindividualinterruptsusingtheinterruptregisterscanprevent

simultaneousoccurrences.

Timer/Event Counter Interrupt

ForaTimer/EventCounterinterrupttooccur,theglobalinterruptenablebit,EMI,andthe

correspondingtimerinterruptenablebit,ET0I/ET1I,mustfirstbeset.AnactualTimer/Event

CounterinterruptwilltakeplacewhentheTimer/EventCounterinterruptrequestflag,T0F/T1F,

isset,asituationthatwilloccurwhentheTimer/EventCounteroverflows.Whentheinterruptis

enabled,thestackisnotfullandaTimer/EventCounteroverflowoccurs,asubroutinecalltothe

timerinterruptvectoratlocation08H/0CH,willtakeplace.Whentheinterruptisserviced,thetimer

interruptrequestflag,T0F/T1F,willbeautomaticallyresetandtheEMIbitwillbeautomatically

clearedtodisableotherinterrupts.

Programming Considerations

Bydisablingtheinterruptenablebits,arequestedinterruptcanbepreventedfrombeingserviced,

however,onceaninterruptrequestflagisset,itwillremaininthisconditionintheinterruptcontrol

registeruntilthecorrespondinginterruptisservicedoruntiltherequestflagisclearedbyasoftware

instruction.

Itisrecommendedthatprogramsdonotusethe"CALLsubroutine"instructionwithintheinterrupt

subroutine.Interruptsoftenoccurinanunpredictablemannerorneedtobeservicedimmediately

insomeapplications.Ifonlyonestackisleftandtheinterruptisnotwellcontrolled,theoriginal

controlsequencewillbedamagedoncea"CALLsubroutine"isexecutedintheinterruptsubroutine.

AlloftheseinterruptshavethecapabilityofwakinguptheprocessorwheninthePowerDown

Mode.

OnlytheProgramCounterispushedontothestack.Ifthecontentsoftheaccumulatororstatus

registerarealteredbytheinterruptserviceprogram,whichmaycorruptthedesiredcontrol

sequence,thenthecontentsshouldbesavedinadvance.

HT82B42R Datasheet(PDF) 38 Page - Holtek Semiconductor Inc

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