HT45F23/HT45F43
8-Bit Flash MCU with Op Amps & Comparators
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
FSTEN
Bit
Wake-up Time
(SLEEP0 Mode)
Wake-up Time
(SLEEP1 Mode)
Wake-up Time
(IDLE0 Mode)
Wake-up Time
(IDLE1 Mode)
Oscillator
0
1024 HXT cycles
1024 HXT cycles
1~2 fSUB cycles
1~2 HXT cycles
HXT
1
1024 HXT cycles
(System runs with fSUB first for 1024 HXT cycles and 1~2 HXT cycles
then switches over to run with the HXT clock)
ERC
EC
X
X
X
X
X
15~16 ERC cycles 15~16 ERC cycles
15~16 EC cycles 15~16 EC cycles
15~16 HIRC cycles 15~16 HIRC cycles
1~2 ERC cycles
1~2 EC cycles
1~2 HIRC cycles
1~2 LIRC cycles
1~2 LXT cycles
HIRC
LIRC
LXT
1~2 LIRC cycles
1024 LTX cycles
1~2 LIRC cycles
1024 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.
Rev. 1.20
43
September 15, 2011
HOLTEK [ HOLTEK SEMICONDUCTOR INC ]
