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Rev. 1.21
42
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Rev. 1.21
43
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HT66F488/HT66F489
A/D Flash MCU with EEPROM
HT66F488/HT66F489
A/D Flash MCU with EEPROM
If the HIRC oscillators or LIRC oscillator is used as the system oscillator then it will take 15~16
clock cycles or 1~2 cycles 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
(SLEEP Mode)
Wake-up Time
(IDLE0 Mode)
Wake-up Time
(IDLE1 Mode)
HXT
�
128 HXT cycles
1~2 HXT cycles
1
1~2 f
SUB
cycles
(Syste� �uns with f
SUB
first for 128 HXT cycles and
then switches ove� to �un with the HXT clock)
1~2 HXT cycles
HIRC
×
15~16 HIRC cycles
1~2 HIRC cycles
LIRC
×
1~2 LIRC cycles
1~2 LIRC cycles
LXT
×
128 LXT cycles
1~2 LXT cycles
Wake-up Times
Operating Mode Switching
The device can switch between operating modes dynamically allowing the user to select the best
performance/power ratio for the present task in hand. In this way microcontroller operations that
do not require high performance can be executed using slower clocks thus requiring less operating
current and prolonging battery life in portable applications.
In simple terms, Mode Switching between the NORMAL Mode and SLOW Mode is executed
using the HLCLK bit and CKS2~CKS0 bits in the SMOD register while Mode Switching from the
NORMAL/SLOW Modes to the SLEEP/IDLE Modes is executed via the HALT instruction. When
a HALT instruction is executed, whether the device enters the IDLE Mode or the SLEEP Mode is
determined by the condition of the IDLEN bit in the SMOD register and FSYSON in the CTRL
register.
When the HLCLK bit switches to a low level, which implies that clock source is switched from the
high speed clock source, f
H
, to the clock source, f
H
/2~f
H
/64 or f
L
. If the clock is from the f
L
, the high
speed clock source will stop running to conserve power. When this happens it must be noted that the
f
H
/16 and f
H
/64 internal clock sources will also stop running, which may affect the operation of other
internal functions such as the TMs. The accompanying flowchart shows what happens when the
device moves between the various operating modes.
NORMAL Mode to SLOW0 Mode Switching
When running in the NORMAL Mode, which uses the high speed system oscillator, and therefore
consumes more power, the system clock can switch to run in the SLOW0 Mode by setting the
HLCLK bit to “0” and setting the CKS2~CKS0 bits to “000” or “001” in the SMOD register.This
will then use the low speed system oscillator which will consume less power. Users may decide to
do this for certain operations which do not require high performance and can subsequently reduce
power consumption. The SLOW Mode is sourced from the LIRC or LXT oscillator and therefore
requires these oscillators to be stable before full mode switching occurs. This is monitored using the
LTO bit in the SMOD register.