HT68F017 datasheet(35/116 Pages) HOLTEK

35 / 116 page

HT66F016/HT66F017/HT68F016/HT68F017

Rev. 1.00

May 14, 2012

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 the LIRC oscillator, to act as a temporary clock

to first drive the system until the original system oscilla-

tor 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/disable 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 oscillator for the system to wake-up. The system

will then initially run under the fSUB clock source until 128

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 HIRC oscillators or LIRC oscillator is used as the

system oscillator then it will take 15~16 clock cycles of

the HIRC or 1~2 cycles of the LIRC to wake up the sys-

tem 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

128 HXT cycles

1~2 HXT cycles

128 HXT cycles

1~2 fSUB cycles

(System runs with fSUB first for 128 HXT cycles and

then switches over to run with the HXT clock)

1~2 HXT cycles

HIRC

15~16 HIRC cycles

1~2 HIRC cycles

LIRC

1~2 LIRC cycles

Wake-Up Times

Note that if the Watchdog Timer is disabled, which means that the LIRC is off, then there will be no Fast Wake-up func-

tion available when the device wakes-up from the SLEEP0 Mode.

Operating Mode Switching and Wake-up

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

²X²: don¢t care

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