HT68F20 datasheet(39/210 Pages) HOLTEK

39 / 210 page

HT68F20/HT68F30/HT68F40/HT68F50/HT68F60

Rev. 1.00

November 3, 2009

Fast Wake-up

To minimise power consumption the device can enter

the SLEEP or IDLE0 Mode, where the system clock

source to the device will be stopped. However when the

device is woken up again, it can take a considerable

time for the original system oscillator to restart, stabilise

and allow normal operation to resume. To ensure the

device is up and running as fast as possible a Fast

Wake-up function is provided, which allows fSUB,

namely either the LXT or LIRC oscillator, to act as a tem-

porary clock to first drive the system until the original

system oscillator has stabilised. As the clock source for

the Fast Wake-up function is fSUB, the Fast Wake-up

function is only available in the SLEEP1 and IDLE0

modes. When the device is woken up from the SLEEP0

mode, the Fast Wake-up function has no effect because

the fSUB clock is stopped. The Fast Wake-up enable/dis-

able function is controlled using the FSTEN bit in the

SMOD register.

If the HXT oscillator is selected as the NORMAL Mode

system clock, and if the Fast Wake-up function is en-

abled, then it will take one to two tSUB clock cycles of the

LIRC or LXT oscillator for the system to wake-up. The

system will then initially run under the fSUB clock source

until 1024 HXT clock cycles have elapsed, at which

point the HTO flag will switch high and the system will

switch over to operating from the HXT oscillator.

If the ERC or HIRC oscillators or LIRC oscillator is used

as the system oscillator then it will take 15~16 clock cy-

cles of the ERC or HIRC or 1~2 cycles of the LIRC to

wake up the system from the SLEEP or IDLE0 Mode.

The Fast Wake-up bit, FSTEN will have no effect in

these cases.

System

Oscillator

FSTEN

Bit

Wake-up Time

(SLEEP0 Mode)

Wake-up Time

(SLEEP1 Mode)

Wake-up Time

(IDLE0 Mode)

Wake-up Time

(IDLE1 Mode)

HXT

1024 HXT cycles

1~2 HXT cycles

1024 HXT cycles

1~2 fSUB cycles

(System runs with fSUB first for 1024 HXT cycles

and then switches over to run with the HXT clock)

1~2 HXT cycles

ERC

15~16 ERC cycles

1~2 ERC cycles

HIRC

15~16 HIRC cycles

1~2 HIRC cycles

LIRC

1~2 LIRC cycles

LXT

1024 LTX cycles

1024 LXT cycles

1~2 LXT cycles

Wake-Up Times

Note that if the Watchdog Timer is disabled, which means that the LXT and LIRC are all both off, then there will be no

Fast Wake-up function available when the device wakes-up from the SLEEP0 Mode.

S L E E P 0

H A L T i n s t r u c t i o n i s e x e c u t e d

f S Y S o f f

C P U s t o p

I D L E N = 0

f T B C o f f

f S U B o f f

W D T & L V D o f f

N O R M A L

f S Y S = f H ~ f H / 6 4

f H o n

C P U r u n

f S Y S o n

f T B C o n

f S U B o n

I D L E 1

H A L T i n s t r u c t i o n i s e x e c u t e d

C P U s t o p

I D L E N = 1

F S Y S O N = 1

f S Y S o n

f T B C o n

f S U B o n

I D L E 0

H A L T i n s t r u c t i o n i s e x e c u t e d

C P U s t o p

I D L E N = 1

F S Y S O N = 0

f S Y S o f f

f T B C o n

f S U B o n

S L O W

f S Y S = f L

f L o n

C P U r u n

f S Y S o n

f T B C o n

f S U B o n

f H o f f

S L E E P 1

H A L T i n s t r u c t i o n i s e x e c u t e d

f S Y S o f f

C P U s t o p

I D L E N = 0

f T B C o f f

f S U B o n

W D T o r L V D o n

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