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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
Bit 1
IDLEN
: IDLE Mode Control
0: Disable
1: Enable
This is the IDLE Mode Control bit and determines what happens when the HALT
instruction is executed. If this bit is high, when a HALT instruction is executed the
device will enter the IDLE Mode. In the IDLE1 Mode the CPU will stop running
but the system clock will continue to keep the peripheral functions operational, if
FSYSON bit is high. If FSYSON bit is low, the CPU and the system clock will all stop
in IDLE0 mode. If the bit is low the device will enter the SLEEP Mode when a HALT
instruction is executed.
Bit 0
HLCLK
: System Clock Selection
0: f
H
/2 ~ f
H
/64 or f
L
1: f
H
This bit is used to select if the f
H
clock or the f
H
/2 ~ f
H
/64 or f
L
clock is used as the
system clock. When the bit is high the f
H
clock will be selected and if low the f
H
/2 ~
f
H
/64 or f
L
clock will be selected. When system clock switches from the f
H
clock to the
f
L
clock and the f
H
clock will be automatically switched off to conserve power.
CTRL Register
Bit
7
6
5
4
3
2
1
0
�a�e
FSYSO�
—
—
—
—
LVRF
LRF
WRF
R/W
R/W
—
—
—
—
R/W
R/W
R/W
POR
�
—
—
—
—
�
�
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B
it 7
FSYSON
:
f
SYS
Control IDLE Mode
0: Disable
1: Enable
Bit 6~ 3
Unimplemented, read as “0”
Bit 2
LVRF
: LVR function reset flag
Describe elsewhere
Bit 1
LRF
: LVRC register software reset flag
Describe elsewhere
Bit 0
WRF
: WDTC register software reset flag
Describe elsewhere
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
SUB
, to act as a temporary clock to first drive the system until the original
system oscillator has stabilised. The temporary clock is sourced by the LIRC or LXT oscillator. As
the clock source for the Fast Wake-up function is f
SUB
, the Fast Wake-up function is only available
in the SLEEP and IDLE0 modes. 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 for the system to wake-up. The
system will then initially run under the f
SUB
clock source until 128 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.