Rev. 1.50
4�
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Rev. 1.50
49
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HT66F0175/HT66F0185
A/D Flash MCU with EEPROM
HT66F0175/HT66F0185
A/D Flash MCU with EEPROM
Fast Wake-up
To minimise power consumption the device can enter the SLEEP or IDLE0 Mode, where the system
clock source to the devices will be stopped. However when the devices are 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 devices are up and running as fast as possible a Fast Wake-
up function is provided, which allows f
SUB
, 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 f
SUB
, the Fast Wake-up function is only available in
the SLEEP1 and IDLE0 modes. When the devices are woken up from the SLEEP0 mode, the Fast
Wake-up function has no effect because the f
SUB
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 t
SUB
clock cycles of the LIRC or LXT oscillator for
the system to wake-up. The system will then initially run under the f
SUB
clock source until 512 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 oscillator 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 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
0
1�� HXT cycles
1�� HXT cycles
1~� HXT cycles
1
1�� HXT cycles
1~� f
SUB
cycles
(System r�ns with f
SUB
first for 512 HXT cycles and
then switches over to r�n with the HXT clock)
1~� HXT cycles
HIRC
x
15~16 HIRC cycles 15~16 HIRC cycles
1~� HIRC cycles
LIRC
x
1~� LIRC cycles
1~� LIRC cycles
1~� LIRC cycles
LXT
x
1�� HXT cycles
1~� LXT cycles
1~� LXT cycles
“x”: don’t care
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 devices wake-up from the SLEEP0
Mode.