HT68F04 Holtek Semiconductor, HT68F04 Datasheet - Page 33

• Manufacturer Part Number: HT68F04
• Description: Small Package Enhanced Flash Type 8-Bit MCU
• Manufacturer: Holtek Semiconductor

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 f
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 f
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 f
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. 1.00
Oscillator
System
SUB
HIRC
LIRC
ERC
HXT
LXT
clock is stopped. The Fast Wake-up enable/dis-
FSTEN
Bit
X
X
X
X
0
1
15~16 HIRC cycles
15~16 ERC cycles
1024 HXT cycles
1024 HXT cycles
1024 LTX cycles
(SLEEP0 Mode)
1~2 LIRC cycles
Wake-up Time
SUB
, the Fast Wake-up
and then switches over to run with the HXT clock)
(System runs with f
Wake-Up Times
(SLEEP1 Mode)
SUB
Wake-up Time
,
HT66F03/HT66F04/HT68F03/HT68F04
33
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 t
LIRC oscillator for the system to wake-up. The system
will then initially run under the f
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.
15~16 HIRC cycles
15~16 ERC cycles
1024 HXT cycles
1~2 LIRC cycles
1024 LXT cycles
1~2 f
SUB
SUB
first for 1024 HXT cycles
cycles
Wake-up Time
(IDLE0 Mode)
SUB
SUB
clock cycles of the
clock source until
1~2 HIRC cycles
1~2 LIRC cycles
1~2 HXT cycles
1~2 HXT cycles
1~2 ERC cycles
1~2 LXT cycles
Wake-up Time
(IDLE1 Mode)
April 16, 2010
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