Holtek BS82B12A-3 - Oscillator; Oscillato� Ove�View; System Clock Configurations

Rev. 1.20 44 January 23, 2015 Rev. 1.20 45 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
Oscillator
Variousoscillatoroptionsoffertheuserawiderangeoffunctionsaccordingtotheirvarious
applicationrequirements.Theflexiblefeaturesoftheoscillatorfunctionsensurethatthebest
optimisationcanbeachievedintermsofspeedandpowersaving.Oscillatorselectionsandoperation
areselectedthroughacombinationofcongurationoptionsandregisters.
Oscillator Overview
Allthedevicesincludetwointernaloscillatorsandthesomedevicesalsoincludeanexternal
oscillator.Inadditiontobeingthesourceofthemainsystemclocktheoscillatorsalsoprovideclock
sourcesfortheWatchdogTimer,TimeBasesandTMs.Externaloscillatorrequiringsomeexternal
componentsaswellasfullyintegratedinternaloscillatorsrequiringnoexternalcomponents,are
providedtoformawiderangeofbothfastandslowsystemoscillators.FortheBS82C16A-3and
BS82D20A-3devices,thelowspeedoscillatorsareselectedthroughthecongurationoption.The
higherfrequencyoscillatorsprovidehigherperformancebutcarrywithitthedisadvantageofhigher
powerrequirements,whiletheoppositeisofcoursetrueforthelowerfrequencyoscillators.With
thecapabilityofdynamicallyswitchingbetweenfastandslowsystemclock,thedeviceshavethe
exibilitytooptimizetheperformance/powerratio,afeatureespeciallyimportantinpowersensitive
portableapplications.
Device Type Name Freq. Pins
BS82B12A-3
BS82C16A-3
BS82D20A-3
Internal High Speed RC HIRC 8/12/16MHz —
Internal Low Speed RC LIRC 32kHz —
BS82C16A-3
BS82D20A-3
External Low Speed Crystal LXT 32768Hz XT1/XT2
Oscillator Types
System Clock Congurations
Therearethreemethodsofgeneratingthesystemclock,ahighspeedoscillatorandtwolowspeed
oscillators.Thehighspeedoscillatoristheinternal8MHz,12MHz,16MHzRCoscillator.Thetwo
lowspeedoscillatorsaretheinternal32kHzoscillator,LIRC,andtheexternal32.768kHzcrystal
oscillator,LXT.Selectingwhethertheloworhighspeedoscillatorisusedasthesystemoscillatoris
implementedusingtheHLCLKbitandCKS2~CKS0bitsintheSMODregisterandasthesystem
clockcanbedynamicallyselected.
Fortwoofthethreedevices,theactualsourceclockusedforthelowspeedoscillatorischosenvia
congurationoption.Thefrequencyoftheslowspeedorhighspeedsystemclockisalsodetermined
usingtheHLCLKbitandCKS2~CKS0bitsintheSMODregister.Notethattwooscillator
selectionsmustbemadenamelyonehighspeedandonelowspeedsystemoscillators.Itisnot
possibletochooseano-oscillatorselectionforeitherthehighorlowspeedoscillator.