HT46R006 datasheet(22/72 Pages) HOLTEK

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HT48R006/HT46R006

Rev. 1.00

October 24, 2011

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.

System 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 functions. External oscillators

requiring some external components as well as a two

fully integrated internal oscillators, requiring no external

components, are provided to form a wide range of both

fast and slow system oscillators.

Type

Name

Freq.

External Crystal

HXT

400kHz~

12MHz

External RC

ERC

400kHz~

12MHz

Internal High Speed RC

HIRC

4,8or

12MHz

External Low Speed Crystal

LXT

32768Hz

Internal Low Speed RC

LIRC

15kHz

System Clock Configurations

There are five system oscillators. Three high speed os-

cillators and two low speed oscillators. The high speed

oscillators are the external crystal/ceramic oscillator -

HXT, the external - ERC, and the internal RC oscillator -

HIRC. The two low speed oscillator are the external

32768Hz oscillator - LXT and the internal 15kHz

(VDD=5V) oscillator - LIRC.

External Crystal/Resonator Oscillator

- HXT

The simple connection of a crystal across OSC1 and

OSC2 will create the necessary phase shift and feed-

back for oscillation. However, for some crystals and

most resonator types, to ensure oscillation and accurate

frequency generation, it is necessary to add two small

value external capacitors, C1 and C2. The exact 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

8pF

10pF

8MHz

8pF

10pF

4MHz

8pF

10pF

1MHz

100pF

Note:

C1 and C2 values are for guidance only.

Crystal Recommended Capacitor Values

External RC Oscillator

- ERC

Using the ERC oscillator only requires that a resistor,

with a value between 24k

W and 1.5MW, is connected

between OSC1 and VDD, and a capacitor is connected

between OSC and ground, providing a low cost oscilla-

tor configuration. It is only the external resistor that de-

termines the oscillation frequency; the external

capacitor has no influence 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 en-

sure that the influence of the power supply voltage, tem-

perature and process variations on the oscillation

frequency are minimised. As a resistance/frequency ref-

erence point, it can be noted that with an external 120K

resistor connected and with a 5V voltage power supply

and temperature of 25 degrees, the oscillator will have a

frequency of 4MHz within a tolerance of 2%. Here only

the OSC1 pin is used, which is shared with I/O pin PA6,

leaving pin PA5 free for use as a normal I/O pin.

P A 6 / O S C 1

4 7 0 p F

V D D

R O S C

P A 5 / O S C 2

External RC Oscillator

- ERC

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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