BS85B12-3/BS85C20-3/BS85C20-5
Touch Key Flash MCU with LCD/LED Driver
Oscillator
Variousꢀoscillatorꢀoptionsꢀofferꢀtheꢀuserꢀaꢀwideꢀrangeꢀofꢀfunctionsꢀaccordingꢀtoꢀtheirꢀvariousꢀ
applicationꢀrequirements.ꢀTheꢀflexibleꢀfeaturesꢀofꢀtheꢀoscillatorꢀfunctionsꢀensureꢀthatꢀtheꢀbestꢀ
optimisationꢀcanꢀbeꢀachievedꢀinꢀtermsꢀofꢀspeedꢀandꢀpowerꢀsaving.ꢀOscillatorꢀselectionsꢀandꢀoperationꢀ
areꢀselectedꢀthroughꢀaꢀcombinationꢀofꢀconfigurationꢀoptionsꢀandꢀregisters.
Oscillator Overview
Inꢀadditionꢀtoꢀbeingꢀtheꢀsourceꢀofꢀtheꢀmainꢀsystemꢀclockꢀtheꢀslowꢀspeedꢀoscillatorsꢀalsoꢀprovideꢀ
clockꢀsourcesꢀforꢀtheꢀWatchdogꢀTimerꢀandꢀTimeꢀBase.ꢀExternalꢀoscillatorsꢀrequiringꢀsomeꢀexternalꢀ
componentsꢀasꢀwellꢀasꢀfullyꢀintegratedꢀꢀinternalꢀꢀoscillators,ꢀꢀrequiringꢀꢀnoꢀꢀexternalꢀcomponents,ꢀareꢀ
providedꢀtoꢀformꢀaꢀwideꢀrangeꢀofꢀbothꢀfastꢀandꢀslowꢀsystemꢀoscillators.ꢀAllꢀoscillatorꢀoptionsꢀareꢀ
selectedꢀꢀthroughꢀꢀꢀregisters.ꢀꢀTheꢀhigherꢀfrequencyꢀoscillatorsꢀprovideꢀhigherꢀperformanceꢀbutꢀcarryꢀ
withꢀitꢀtheꢀdisadvantageꢀofꢀhigherꢀpowerꢀrequirements,ꢀwhileꢀtheꢀoppositeꢀisꢀofꢀcourseꢀtrueꢀforꢀtheꢀ
lowerꢀfrequencyꢀoscillators.ꢀWithꢀtheꢀcapabilityꢀofꢀdynamicallyꢀꢀswitchingꢀꢀbetweenꢀꢀfastꢀꢀandꢀꢀslowꢀ
systemꢀclock,ꢀtheꢀdeviceꢀhasꢀtheꢀflexibilityꢀtoꢀoptimizeꢀtheꢀperformance/powerꢀꢀratio,ꢀꢀaꢀꢀfeatureꢀ
especiallyꢀꢀimportantꢀꢀinꢀpowerꢀsensitiveꢀportableꢀapplications.
Pins
Device
Type
Name
HIRC
LIRC
LXT
Freq.
8,12ꢀorꢀ16MHz
32kHz
Internal Hiꢁh Speed
Internal Low Speed
External Low Speed
—
—
�ll
OSC1/OSC2
BS85C20-5
32.768kHz
Oscillator Types
System Clock Configurations
Thereꢀareꢀtwoꢀmethodsꢀofꢀgeneratingꢀtheꢀsystemꢀclock,ꢀaꢀhighꢀspeedꢀinternalꢀclockꢀsourceꢀandꢀlowꢀ
speedꢀinternalꢀclockꢀsource.ꢀTheꢀhighꢀspeedꢀoscillatorꢀisꢀanꢀinternalꢀ8MHz,ꢀ12MHzꢀorꢀ16MHzꢀRCꢀ
oscillatorꢀwhileꢀtheꢀlowꢀspeedꢀoscillatorꢀisꢀanꢀinternalꢀ32kHzꢀRCꢀoscillator.ꢀBothꢀoscillatorsꢀareꢀ
fullyꢀintegratedꢀandꢀdoꢀnotꢀrequireꢀexternalꢀcomponents.ꢀSelectingꢀwhetherꢀtheꢀlowꢀorꢀhighꢀspeedꢀ
oscillatorꢀisꢀusedꢀasꢀtheꢀꢀsystemꢀꢀoscillatorꢀꢀisꢀꢀimplementedꢀꢀusingꢀꢀtheꢀHLCLKꢀbitꢀandꢀCKS2ꢀ~ꢀ
CKS0ꢀbitsꢀinꢀtheꢀSMODꢀregisterꢀallowingꢀtheꢀsystemꢀclockꢀtoꢀbeꢀdynamicallyꢀselected.
Internal High Speed RC Oscillator – HIRC
TheꢀinternalꢀHighꢀSpeedꢀRCꢀoscillatorꢀisꢀaꢀfullyꢀintegratedꢀsystemꢀoscillatorꢀrequiringꢀnoꢀexternalꢀ
components.ꢀTheꢀinternalꢀRCꢀoscillatorꢀhasꢀaꢀpowerꢀonꢀdefaultꢀfrequencyꢀofꢀ8ꢀMHzꢀbutꢀcanꢀbeꢀ
selectedꢀtoꢀbeꢀeitherꢀ8MHz,ꢀ12MHzꢀorꢀ16MHzꢀusingꢀtheꢀHIRCS1ꢀandꢀHIRCS0ꢀbitsꢀinꢀtheꢀCTRLꢀ
register.ꢀDeviceꢀtrimmingꢀduringꢀtheꢀmanufacturingꢀprocessꢀandꢀtheꢀinclusionꢀofꢀinternalꢀfrequencyꢀ
compensationꢀcircuitsꢀareꢀusedꢀtoꢀensureꢀthatꢀtheꢀinfluenceꢀofꢀtheꢀpowerꢀsupplyꢀvoltage,ꢀtemperatureꢀ
andꢀprocessꢀvariationsꢀonꢀtheꢀoscillationꢀfrequencyꢀareꢀminimised.
Rev. 1.20
42
�ꢀꢁꢀst 10ꢂ 2012
HOLTEK [ HOLTEK SEMICONDUCTOR INC ]
