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Rev. 2.50
58
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Rev. 2.50
59
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HT66F20/HT66F30/HT66F40/HT66F50/HT66F60
HT66FU30/HT66FU40/HT66FU50/HT66FU60
A/D Flash MCU with EEPROM
HT66F20/HT66F30/HT66F40/HT66F50/HT66F60
HT66FU30/HT66FU40/HT66FU50/HT66FU60
A/D Flash MCU with EEPROM
• IDLE0 Mode
The IDLE0 Mode is entered when a HALT instruction is executed and when the IDLEN bit in
the SMOD register is high and the FSYSON bit in the WDTC register is low. In the IDLE0 Mode
the system oscillator will be inhibited from driving the CPU but some peripheral functions will
remain operational such as the Watchdog Timer, TMs and SIM. In the IDLE0 Mode, the system
oscillator will be stopped. In the IDLE0 Mode the Watchdog Timer clock, f
S
, will either be on or
off depending upon the f
S
clock source. If the source is f
SYS
/4 then the f
S
clock will be off, and if
the source comes from f
SUB
then f
S
will be on.
• IDLE1 Mode
The IDLE1 Mode is entered when an HALT instruction is executed and when the IDLEN bit
in the SMOD register is high and the FSYSON bit in the WDTC register is high. In the IDLE1
Mode the system oscillator will be inhibited from driving the CPU but may continue to provide a
clock source to keep some peripheral functions operational such as the Watchdog Timer, TMs and
SIM. In the IDLE1 Mode, the system oscillator will continue to run, and this system oscillator
may be high speed or low speed system oscillator. In the IDLE1 Mode the Watchdog Timer
clock, f
S
, will be on. If the source is f
SYS
/4 then the f
S
clock will be on, and if the source comes
from f
SUB
then f
S
will be on.
Control Register
A single register, SMOD, is used for overall control of the internal clocks within the device.
SMOD Register
Bit
7
6
5
4
3
2
1
0
Name
CKS2
CKS�
CKS0
FSTEN
LTO
HTO
IDLEN
HLCLK
R/W
R/W
R/W
R/W
R/W
R
R
R/W
R/W
POR
0
0
0
0
0
0
�
�
Bit 7~5
CKS2~CKS0
: The system clock selection when HLCLK is "0"
000: f
L
(f
LXT
or f
LIRC
)
001: f
L
(f
LXT
or f
LIRC
)
010: f
H
/64
011: f
H
/32
100: f
H
/16
101: f
H
/8
110: f
H
/4
111: f
H
/2
These three bits are used to select which clock is used as the system clock source. In
addition to the system clock source, which can be either the LXT or LIRC, a divided
version of the high speed system oscillator can also be chosen as the system clock
source.
Bit 4
FSTEN
: Fast Wake-up Control (only for HXT)
0: Disable
1: Enable
This is the Fast Wake-up Control bit which determines if the f
SUB
clock source is
initially used after the device wakes up. When the bit is high, the f
SUB
clock source can
be used as a temporary system clock to provide a faster wake up time as the f
SUB
clock
is available.