HT68F20 datasheet(33/210 Pages) HOLTEK

33 / 210 page

HT68F20/HT68F30/HT68F40/HT68F50/HT68F60

Rev. 1.00

November 3, 2009

Oscillator

Various oscillator options offer the user a wide range of

functions according to their various application require-

ments. 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

configuration options and registers.

Oscillator Overview

In addition to being the source of the main system clock

the oscillators also provide clock sources for the Watch-

dog Timer and Time Base Interrupts. External oscilla-

tors 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. All oscillator options

are selected through the configuration options. The

higher frequency oscillators provide higher performance

but carry with it the disadvantage of higher power re-

quirements, while the opposite is of course true for the

lower frequency oscillators. With the capability of dy-

namically switching between fast and slow system

clock, the device has the flexibility to optimize the perfor-

mance/power ratio, a feature especially important in

power sensitive portable applications.

Type

Name

Freq.

Pins

External Crystal

HXT

400kHz~

20MHz

OSC1/

OSC2

External RC

ERC

8MHz

OSC1

Internal High

Speed RC

HIRC

4, 8 or 12MHz

External Low

Speed Crystal

LXT

32.768kHz

XT1/

XT2

Internal Low

Speed RC

LIRC

32kHz

Oscillator Types

System Clock Configurations

There are five methods of generating the system clock,

three high speed oscillators and two low speed oscilla-

tors. The high speed oscillators are the external crystal/

ceramic oscillator, external RC network oscillator and

the internal 4MHz, 8MHz or 12MHz RC oscillator. The

two low speed oscillators are the internal 32kHz RC os-

cillator and the external 32.768kHz crystal oscillator. Se-

lecting 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.

HXT

ERC

HIRC

LIRC

LXT

6-stage Prescaler

High Speed Oscillation

Low Speed Oscillation

Configuration Option

High Speed Oscillation

Configuration Option

fH/2

fH/4

fH/8

fH/16

fH/32

fH/64

HLCLK,

CKS2~CKS0 bits

Fast Wake-up from SLEEP Mode or

IDLE Mode Control (for HXT only)

fSYS

fSUB

System Clock Configurations

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