Holtek HT66F0175 - Standby C�Rrent Considerations; Wake-�P

Rev. 1.50 54 August 28, 2017 Rev. 1.50 55 August 28, 2017
HT66F0175/HT66F0185
A/D Flash MCU with EEPROM
HT66F0175/HT66F0185
A/D Flash MCU with EEPROM
Standby Current Considerations
AsthemainreasonforenteringtheSLEEPorIDLEModeistokeepthecurrentconsumptionofthe
devicetoaslowavalueaspossible,perhapsonlyintheorderofseveralmicro-ampsexceptinthe
IDLE1Mode,thereareotherconsiderationswhichmustalsobetakenintoaccountbythecircuit
designerifthepowerconsumptionistobeminimised.SpecialattentionmustbemadetotheI/Opins
onthedevice.Allhigh-impedanceinputpinsmustbeconnectedtoeitheraxedhighorlowlevelas
anyoatinginputpinscouldcreateinternaloscillationsandresultinincreasedcurrentconsumption.
Thisalsoappliestodeviceswhichhavedifferentpackagetypes,astheremaybeunbonbedpins.
Thesemusteitherbesetupasoutputsorifsetupasinputsmusthavepull-highresistorsconnected.
Caremustalsobetakenwiththeloads,whichareconnectedtoI/Opins,whicharesetupasoutputs.
Theseshouldbeplacedinaconditioninwhichminimumcurrentisdrawnorconnectedonlyto
externalcircuitsthatdonotdrawcurrent,suchasotherCMOSinputs.Alsonotethatadditional
standbycurrentwillalsoberequirediftheLIRCoscillatorhasenabled.
IntheIDLE1Modethesystemoscillatorison,ifthesystemoscillatorisfromthehighspeed
oscillator,theadditionalstandbycurrentwillalsobeperhapsintheorderofseveralhundredmicro-
amps.
Wake-up
TominimisepowerconsumptionthedevicecanentertheSLEEPoranyIDLEMode,wherethe
CPUwillbeswitchedoff.However,whenthedeviceiswokenupagain,itwilltakeaconsiderable
timefortheoriginalsystemoscillatortorestart,stabliseandallownormaloperationtoresume.
AfterthesystementerstheSLEEPorIDLEMode,itcanbewokenupfromoneofvarioussources
listedasfollows:
• AnexternalfallingedgeonPortA
• Asysteminterrupt
• AWDToverow
Whenthedevicesexecutethe“HALT”instruction,itwillenterthePowerdownmodeandthePDF
agwillbesetto1.ThePDFagwillbeclearedto0ifthedevicesexperienceasystempower-up
orexecutestheclearWatchdogTimerinstruction.IfthesystemiswokenupbyaWDToverow,a
WatchdogTimerresetwillbeinitiatedandtheTOagwillbesetto1.TheTOagissetifaWDT
time-outoccursandcausesawake-upthatonlyresetstheProgramCounterandStackPointer,other
agsremainintheiroriginalstatus.
EachpinonPortAcanbesetupusingthePAWUregistertopermitanegativetransitiononthepin
towakeupthesystem.WhenaPortApinwake-upoccurs,theprogramwillresumeexecutionat
theinstructionfollowingthe“HALT”instruction.Ifthesystemiswokenupbyaninterrupt,then
twopossiblesituationsmayoccur.Therstiswheretherelatedinterruptisdisabledortheinterrupt
isenabledbutthestackisfull,inwhichcasetheprogramwillresumeexecutionattheinstruction
followingthe“HALT”instruction.Inthissituation,theinterruptwhichwokeupthedeviceswillnot
beimmediatelyserviced,butwillratherbeservicedlaterwhentherelatedinterruptisnallyenabled
orwhenastacklevelbecomesfree.Theothersituationiswheretherelatedinterruptisenabledand
thestackisnotfull,inwhichcasetheregularinterruptresponsetakesplace.Ifaninterruptrequest
flagissethighbeforeenteringtheSLEEPorIDLEMode,thewake-upfunctionoftherelated
interruptwillbedisabled.