HT95R22 datasheet(28/52 Pages) HOLTEK

28 / 52 page

HT95R22

Rev. 1.00

January 6, 2009

Oscillator

There are two oscillator circuits within the controller. One is for the system clock which uses an externally connected

32768Hz crystal. The other is an internal watchdog oscillator.

System Crystal/Ceramic Oscillator

The system clock is generated using an external 32768Hz crystal or ceramic resonator connected between pins X1

and X2. From this clock source an internal circuit generates a 3.58MHz clock source which is also required by the sys-

tem. This frequency generator circuit requires the addition of externally connected RC components to pin XC to form a

low pass filter for the 3.58MHz output frequency stabilisation.

Watchdog Timer Oscillator

The WDT oscillator is a fully integrated free running RC oscillator with a typical period of 65

ms at 5V, requiring no exter-

nal components. It is selected via configuration option. If selected, when the device enters the Power Down Mode, the

system clock will stop running, however the WDT oscillator will continue to run and keep the watchdog function active.

However, as the WDT will consume a certain amount of power when in the Power Down Mode, for low power applica-

tions, it may be desirable to disable the WDT oscillator by configuration option.

Operation Mode, Power-down and Wake-up

There are four operational modes, known as the idle mode, sleep mode, green mode, and normal mode. The chosen

mode is selected using the MODE0, MODE1 and UPEN bits in the MODE register but also depends upon whether the

HALT instruction has been executed or not.

X 1

X 2

X C

1 5 k W

3 n F

4 7 n F

Crystal/Ceramic Oscillator

HALT

Instruction

MODE1

MODE0

UPEN

Operation

Mode

32768Hz

3.58MHz

System

Clock

Not executed

Normal

3.58MHz

Not executed

Green

OFF

32768Hz

Executed

Sleep

OFF

Stopped

Executed

Idle

OFF

Stopped

Note:

²X² means don¢t care

MODE0 will be cleared to 0 automatically after wake-up from Idle Mode.

M O D E R e g i s t e r

b 7

b 0

N o t i m p l e m e n t e d , r e a d a s " 0 "

M O D E 1 M O D E 0 U P E N

F r e q u e n c y u p c o n v e r s i o n t o g e n e r a t e 3 . 5 8 M H z e n a b l e

1 : e n a b l e

0 : d i s a b l e

3 2 7 6 8 H z o s c i l l a t o r e n a b l e w h i l e t h e H A L T i n s t r u c t i o n i s e x e c u t e

1 : d i s a b l e 3 2 7 6 8 H z o s c i l l a t o r ( I d l e m o d e )

0 : e n a b l e 3 2 7 6 8 H z o s c i l l a t o r ( S l e e p m o d e )

S y s t e m c l o c k s e l e c t

1 : s e l e c t 3 . 5 8 M H z a s C P U c l o c k s y s t e m

0 : s e l e c t 3 2 7 6 8 H z a s C P U c l o c k s y s t e m

MODE Register

HT95R22 Datasheet(PDF) 28 Page - Holtek Semiconductor Inc

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