Rev. 1.50
46
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Rev. 1.50
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HT66F0175/HT66F0185
A/D Flash MCU with EEPROM
HT66F0175/HT66F0185
A/D Flash MCU with EEPROM
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 CTRL 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 and TMs. In the IDLE1
Mode, the system oscillator will continue to run, and this system oscillator may be high speed or low
speed system oscillator.
Control Registers
A single register, SMOD, is used for overall control of the internal clocks within the devices.
SMOD Register
Bit
7
6
5
4
3
2
1
0
Name
CKS�
CKS1
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
1
1
Bit 7~5
CKS2~CKS0
: System clock selection when HLCLK is “0”
000: f
SUB
001: f
SUB
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.
Bit 3
LTO
: Low speed system oscillator ready flag
0: Not ready
1: Ready
This is the low speed system oscillator ready flag which indicates when the low speed
system oscillator is stable after power on reset or a wake-up has occurred. The flag
will be low when in the SLEEP0 Mode but after a wake-up has occurred, the flag will
change to a high level after 128 clock cycles if the LXT oscillator is used and 1~2
clock cycles if the LIRC oscillator is used.