Holtek BS82B12A-3 - Inte; P�Og�Amming Conside�Ations

Rev. 1.20 140 January 23, 2015 Rev. 1.20 141 January 23, 2015
BS82B12A-3/BS82C16A-3/BS82D20A-3
Touch Key 8-Bit Flash MCU with LED/LCD Driver
BS82B12A-3/BS82C16A-3/BS82D20A-3
Touch Key 8-Bit Flash MCU with LED/LCD Driver
Interrupt Wake-up Function
Eachoftheinterruptfunctionshasthecapabilityofwakingupthemicrocontrollerwheninthe
SLEEPorIDLEMode.Awake-upisgeneratedwhenaninterruptrequestagchangesfromlowto
highandisindependentofwhethertheinterruptisenabledornot.Therefore,eventhoughthedevice
isintheSLEEPorIDLEModeanditssystemoscillatorstopped,situationssuchasexternaledge
transitionsontheexternalinterruptpinoralowpowersupplyvoltagemaycausetheirrespective
interruptagtobesethighandconsequentlygenerateaninterrupt.Caremustthereforebetakenif
spuriouswake-upsituationsaretobeavoided.Ifaninterruptwake-upfunctionistobedisabledthen
thecorrespondinginterruptrequestagshouldbesethighbeforethedeviceenterstheSLEEPor
IDLEMode.Theinterruptenablebitshavenoeffectontheinterruptwake-upfunction.
Programming Considerations
Bydisablingtherelevantinterruptenablebits,arequestedinterruptcanbepreventedfrombeing
serviced,however,onceaninterruptrequestflagisset,itwillremaininthisconditioninthe
interruptregisteruntilthecorrespondinginterruptisservicedoruntiltherequestagisclearedby
theapplicationprogram.
Itisrecommendedthatprogramsdonotusethe"CALL"instructionwithintheinterruptservice
subroutine.Interruptsoftenoccurinanunpredictablemannerorneedtobeservicedimmediately.
Ifonlyonestackisleftandtheinterruptisnotwellcontrolled,theoriginalcontrolsequencewillbe
damagedonceaCALLsubroutineisexecutedintheinterruptsubroutine.
EveryinterrupthasthecapabilityofwakingupthemicrocontrollerwhenitisinSLEEPorIDLE
Mode,thewakeupbeinggeneratedwhentheinterruptrequestagchangesfromlowtohigh.Ifitis
requiredtopreventacertaininterruptfromwakingupthemicrocontrollerthenitsrespectiverequest
agshouldberstsethighbeforeenterSLEEPorIDLEMode.
AsonlytheProgramCounterispushedontothestack,thenwhentheinterruptisserviced,ifthe
contentsoftheaccumulator,statusregisterorotherregistersarealteredbytheinterruptservice
program,theircontentsshouldbesavedtothememoryatthebeginningoftheinterruptservice
routine.
Toreturnfromaninterruptsubroutine,eitheraRETorRETIinstructionmaybeexecuted.TheRETI
instructioninadditiontoexecutingareturntothemainprogramalsoautomaticallysetstheEMI
bithightoallowfurtherinterrupts.TheRETinstructionhoweveronlyexecutesareturntothemain
programleavingtheEMIbitinitspresentzerostateandthereforedisablingtheexecutionoffurther
interrupts.