HT66F016 datasheet(31/116 Pages) HOLTEK

31 / 116 page

HT66F016/HT66F017/HT68F016/HT68F017

Rev. 1.00

May 14, 2012

The actual source clock used for each of the high speed

oscillator is chosen via configuration options. The fre-

quency 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 selec-

tions 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. The OSC1 and OSC2 pins are used to con-

nect the external components for the external crystal.

External Crystal/Ceramic Oscillator

- HXT

The External Crystal/ Ceramic System Oscillator is one

of the high frequency oscillator choices, which is se-

lected via configuration option. For most crystal oscilla-

tor configurations, the simple connection of a crystal

across OSC1 and OSC2 will create the necessary

phase shift and feedback for oscillation, without requir-

ing external capacitors. However, for some crystal types

and frequencies, to ensure oscillation, it may be neces-

sary to add two small value capacitors, C1 and C2.

Using a ceramic resonator will usually require two small

value capacitors, C1 and C2, to be connected as shown

for oscillation to occur. The values of C1 and C2 should

be selected in consultation with the crystal or resonator

manufacturer

¢s specification.

Crystal Oscillator C1 and C2 Values

Crystal Frequency

12MHz

0pF

8MHz

0pF

4MHz

0pF

1MHz

100pF

Note:

C1 and C2 values are for guidance only.

Crystal Recommended Capacitor Values

Internal RC Oscillator

- HIRC

The internal RC oscillator is a fully integrated system os-

cillator requiring no external components. The internal

RC oscillator has a fixed frequency of 8MHz. Device

trimming during the manufacturing process and the in-

clusion of internal frequency compensation circuits are

used to ensure that the influence of the power supply

voltage, temperature and process variations on the os-

cillation frequency are minimised. As a result, at a power

supply of 5V and at a temperature of -40

°C ~85°Cde-

grees, the fixed oscillation frequency of the high speed

internal 8MHz RC oscillator will have a tolerance within

2%. Note that if this internal system clock option is se-

lected as the high speed oscillator, as it requires no ex-

ternal pins for its operation, I/O pins PA6 and PA5 can

only be used as normal I/O pins.

Internal 32kHz Oscillator

- LIRC

The Internal 32kHz System Oscillator is the low fre-

quency oscillator. It is a fully integrated RC oscillator

with a typical frequency of 32kHz at 5V, requiring no ex-

ternal components for its implementation. Device trim-

ming during the manufacturing process and the

inclusion of internal frequency compensation circuits

are used to ensure that the influence of the power sup-

ply voltage, temperature and process variations on the

oscillation frequency are minimised. As a result, at a

power supply of 5V and at a temperature of 25

°Cde-

grees, the fixed oscillation frequency of 32kHz will have

a tolerance within 10%.

Supplementary Oscillators

The low speed oscillators, in addition to providing a sys-

tem clock source are also used to provide a clock

source to two other device functions. These are the

Watchdog Timer and the Time Base Interrupts.

O S C 1

O S C 2

R f

T o i n t e r n a l

c i r c u i t s

I n t e r n a l

O s c i l l a t o r

C i r c u i t

C 1

C 2

R p

N o t e : 1 . R p i s n o r m a l l y n o t r e q u i r e d . C 1 a n d C 2 a r e r e q u i r e d .

2 . A l t h o u g h n o t s h o w n O S C 1 / O S C 2 p i n s h a v e a p a r a s i t i c

c a p a c i t a n c e o f a r o u n d 7 p F .

Crystal/Resonator Oscillator

- HXT

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