HT45F75 datasheet(57/190 Pages) HOLTEK

57 / 190 page

Rev. 1.10

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HT45F75

Body Fat Scale Flash MCU

HT45F75

Body Fat Scale Flash MCU

Programming Considerations

TheHXTandLXToscillatorsbothusethesameSSTcounter.Forexample,ifthesystemiswoken

upfromtheSLEEP0ModeandboththeHXTandLXToscillatorsneedtostart-upfromanoffstate.

TheLXToscillatorusestheSSTcounterafterHXToscillatorhasfinisheditsSSTperiod.

• IfthedeviceiswokenupfromtheSLEEP0ModetotheNORMALMode,thehighspeedsystem

oscillatorneedsanSSTperiod.ThedevicewillexecutefirstinstructionafterHTOis“1”.Atthis

time,theLXToscillatormaynotbestabilityiffSUBisfromLXToscillator.Thesamesituation

occursinthepower-onstate.TheLXToscillatorisnotreadyyetwhenthefirstinstructionis

executed.

• IfthedeviceiswokenupfromtheSLEEP1ModetoNORMALMode,andthesystemclock

sourceisfromHXToscillatorandFSTENis“1”,thesystemclockcanbeswitchedtotheLXT

orLIRCoscillatorafterwakeup.

• Thereareperipheralfunctions,suchasWDT,TMsandSIM,forwhichthefSYSisused.Ifthe

systemclocksourceisswitchedfromfHtofSUB,theclocksourcetotheperipheralfunctions

mentionedabovewillchangeaccordingly.

Watchdog Timer

TheWatchdogTimerisprovidedtopreventprogrammalfunctionsorsequencesfromjumpingto

unknownlocations,duetocertainuncontrollableexternaleventssuchaselectricalnoise.

Watchdog Timer Clock Source

TheWatchdogTimerclocksourceisprovidedbytheinternalclock,fS,whichisinturnsuppliedby

oneoftwosourcesselectedbyconfigurationoption:fSUBorfSYS/4.ThefSUBclockcanbesourced

fromeithertheLXTorLIRCoscillators,againchosenviaaconfigurationoption.TheWatchdog

Timersourceclockisthensubdividedbyaratioof28to218togivelongertimeouts,theactualvalue

beingchosenusingtheWS2~WS0bitsintheWDTCregister.TheLIRCinternaloscillatorhas

anapproximateperiodof32kHzatasupplyvoltageof5V.However,itshouldbenotedthatthis

specifiedinternalclockperiodcanvarywithVDD,temperatureandprocessvariations.TheLXT

oscillatorissuppliedbyanexternal32.768kHzcrystal.TheotherWatchdogTimerclocksource

optionisthefSYS/4clock.

Watchdog Timer Control Register

Asingleregister,WDTC,controlstherequiredtimeoutperiodaswellastheenable/disable

operation.Thisregistertogetherwithseveralconfigurationoptionscontroltheoveralloperationof

theWatchdogTimer.

HT45F75 Datasheet(PDF) 57 Page - Holtek Semiconductor Inc