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Rev. 2.50 52 June 22, 2017 Rev. 2.50 53 June 22, 2017

HT66F20/HT66F30/HT66F40/HT66F50/HT66F60

HT66FU30/HT66FU40/HT66FU50/HT66FU60

A/D Flash MCU with EEPROM

HT66F20/HT66F30/HT66F40/HT66F50/HT66F60

HT66FU30/HT66FU40/HT66FU50/HT66FU60

A/D Flash MCU with EEPROM

External RC Oscillator – ERC

UsingtheERCoscillatoronlyrequiresthataresistor,withavaluebetween56kΩand2.4MΩis

connectedbetweenOSC1andVDD,andacapacitorisconnectedbetweenOSC1andground,

providingalowcostoscillatorconfiguration.Itisonlytheexternalresistorthatdeterminesthe

oscillationfrequency;theexternalcapacitorhasnoinuenceoverthefrequencyandisconnected

forstabilitypurposesonly.Devicetrimmingduringthemanufacturingprocessandtheinclusion

ofinternalfrequencycompensationcircuitsareusedtoensurethattheinfluenceofthepower

supplyvoltage,temperatureandprocessvariationsontheoscillationfrequencyareminimised.Asa

resistance/frequencyreferencepoint,itcanbenotedthatwithanexternal120kΩresistorconnected

andwitha5Vvoltagepowersupplyandtemperatureof25˚Cdegrees,theoscillatorwillhavea

frequencyof8MHzwithinatoleranceof2%.HereonlytheOSC1pinisused,whichissharedwith

I/OpinPB1,leavingpinPB2freeforuseasanormalI/Opin.

Foroscillatorstabilityandtominimisetheeffectsofnoiseandcrosstalk,itisimportanttolocatethe

capacitorandresistorasclosetotheMCUaspossible.













External RC Oscillator – ERC

Internal High Speed RC Oscillator – HIRC

TheinternalRCoscillatorisafullyintegratedsystemoscillatorrequiringnoexternalcomponents.

TheinternalRCoscillatorhasthreexedfrequenciesofeither4MHz,8MHzor12MHz.Device

trimmingduringthemanufacturingprocessandtheinclusionofinternalfrequencycompensation

circuitsareusedtoensurethattheinuenceofthepowersupplyvoltage,temperatureandprocess

variationsontheoscillationfrequencyareminimised.Asaresult,atapowersupplyofeither3Vor

5Vandatatemperatureof25˚Cdegrees,thexedoscillationfrequencyof4MHz,8MHzor12MHz

willhaveatolerancewithin2%.Notethatifthisinternalsystemclockoptionisselected,asit

requiresnoexternalpinsforitsoperation,I/OpinsPB1andPB2arefreeforuseasnormalI/Opins.

Holtek HT66F30 User Manual

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