HT45F23 datasheet(43/152 Pages) HOLTEK

43 / 152 page

Bit 0

HLCLK: system clock selection

0: fH/2~fH/64 or fL

1: fH

This bit is used to select if the fH clock or the fH/2~fH/64 or fL clock is used as the system

clock. When the bit is high the fH clock will be selected and if low the fH/2~fH/64 or fL clock will

be selected. When system clock switches from the fH clock to the fL clock and the fH clock will

be automatically switched off to conserve power.

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 temporary 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/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 enabled, 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, EC or HIRC oscillators or LIRC oscillator is used as the system oscillator then it will take

15~16 clock cycles of the ERC, EC 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

15~16 EC cycles

1~2 EC 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.

HT45F23/HT45F43

8-Bit Flash MCU with Op Amps & Comparators

Rev. 1.20

September 15, 2011

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