HT45R22E datasheet(21/72 Pages) HOLTEK

21 / 72 page

HT45R22E

Rev. 1.00

March 17, 2010

Timing Diagram

Note: The write cycle time tWR is the time from a valid stop condition of a write sequence to the end of the valid start con-

dition of sequential command.

t F

t L O W

t R

t H I G H

t S U : S T A

t H D : S T A

t S P

t H D : D A T

t S U : D A T

t S U : S T O

t B U F

V a l i d

S C L

S D A

O U T

t A A

t W R

S C L

S D A

8 t h b i t

A C K

W o r d n

S t o p

C o n d i t i o n

S t a r t

C o n d i t i o n

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 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.

Pins

External Crystal

HXT

400kHz~

4MHz

OSC1/

OSC2

External RC

ERC

400kHz~

4MHz

OSC1

Internal High

Speed RC

HIRC

4095kHz

External Low

Speed Crystal

LXT

32768Hz

OSC1/

OSC2

XT1/

XT2*

Internal Low

Speed RC

LIRC

10kHz

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 10kHz

(VDD=3V) 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.

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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