Holtek HT66F0175 - Operating Modes and System Clocks; System Clocks

Rev. 1.50 44 August 28, 2017 Rev. 1.50 45 August 28, 2017
HT66F0175/HT66F0185
A/D Flash MCU with EEPROM
HT66F0175/HT66F0185
A/D Flash MCU with EEPROM
Operating Modes and System Clocks
Presentdayapplicationsrequirethattheirmicrocontrollershavehighperformancebutoftenstill
demandthattheyconsumeaslittlepoweraspossible,conictingrequirementsthatareespecially
trueinbatterypoweredportableapplications.Thefastclocksrequiredforhighperformancewill
bytheirnatureincreasecurrentconsumptionandofcoursevice-versa,lowerspeedclocksreduce
currentconsumption.AsHoltekhasprovidedthesedeviceswithbothhighandlowspeedclock
sourcesandthemeanstoswitchbetweenthemdynamically,theusercanoptimisetheoperationof
theirmicrocontrollertoachievethebestperformance/powerratio.
System Clocks
ThedeviceshavemanydifferentclocksourcesforboththeCPUandperipheralfunctionoperation.
Byprovidingtheuserwithawiderangeofclockoptionsusingcongurationoptionsandregister
programming,aclocksystemcanbeconguredtoobtainmaximumapplicationperformance.
Themainsystemclock,cancomefromeitherahighfrequencyf
H
orlowfrequencyf
SUB
source,and
isselectedusingtheHLCLKbitandCKS2~CKS0bitsintheSMODregister.Thehighspeedsystem
clockcanbesourcedfromeitheranHXTorHIRCoscillator,selectedviaacongurationoption.
Thelowspeedsystemclocksourcecanbesourcedfrominternalclockf
SUB
.Iff
SUB
isselectedthenit
canbesourcedbyeithertheLXTorLIRCoscillator,selectedviaacongurationoption.Theother
choice,whichisadividedversionofthehighspeedsystemoscillatorhasarangeoff
H
/2~f
H
/64.
Therearetwoadditionalinternalclocksfortheperipheralcircuits,thesubstituteclock,f
SUB
,and
theTimeBaseclock,f
TBC
.EachoftheseinternalclocksissourcedbyeithertheLXTorLIRC
oscillators,selectedviacongurationoptions.Thef
SUB
clockisusedtoprovideasubstituteclockfor
themicrocontrollerjustafterawake-uphasoccurredtoenablefasterwake-uptimes.
HIRC
Prescaler
f
H
LXT
High Speed
Oscillator
Low Speed
Oscillator
f
H
/2
f
H
/16
f
H
/64
f
H
/8
f
H
/4
f
H
/32
HLCLK,
CKS2~CKS0
f
SYS
f
SUB
f
SUB
LIRC
HXT
f
H
High Speed Oscillator
Configuration Option
Low Speed Oscillator
Configuration Option
Fast Wake-up from IDLE
or SLEEP Mode Control
(for HXT only )
f
SUB
IDLEN
f
TBC
f
SYS
/4
TBCK
f
TB
Time Base
WDT
f
SUB
f
TBC
Device Clock Congurations
Note:Whenthesystemclocksourcef
SYS
isswitchedtof
SUB
fromf
H
,thehighspeedoscillatorwill
stoptoconservethepower.Thusthereisnof
H
~f
H
/64forperipheralcircuittouse.