Rev. 1.50
44
����st ��� �01�
Rev. 1.50
45
����st ��� �01�
HT66F0175/HT66F0185
A/D Flash MCU with EEPROM
HT66F0175/HT66F0185
A/D Flash MCU with EEPROM
Operating Modes and System Clocks
Present day applications require that their microcontrollers have high performance but often still
demand that they consume as little power as possible, conflicting requirements that are especially
true in battery powered portable applications. The fast clocks required for high performance will
by their nature increase current consumption and of course vice-versa, lower speed clocks reduce
current consumption. As Holtek has provided these devices with both high and low speed clock
sources and the means to switch between them dynamically, the user can optimise the operation of
their microcontroller to achieve the best performance/power ratio.
System Clocks
The devices have many different clock sources for both the CPU and peripheral function operation.
By providing the user with a wide range of clock options using configuration options and register
programming, a clock system can be configured to obtain maximum application performance.
The main system clock, can come from either a high frequency f
H
or low frequency f
SUB
source, and
is selected using the HLCLK bit and CKS2~CKS0 bits in the SMOD register. The high speed system
clock can be sourced from either an HXT or HIRC oscillator, selected via a configuration option.
The low speed system clock source can be sourced from internal clock f
SUB
. If f
SUB
is selected then it
can be sourced by either the LXT or LIRC oscillator, selected via a configuration option. The other
choice, which is a divided version of the high speed system oscillator has a range of f
H
/2~ f
H
/64.
There are two additional internal clocks for the peripheral circuits, the substitute clock, f
SUB
, and
the Time Base clock, f
TBC
. Each of these internal clocks is sourced by either the LXT or LIRC
oscillators, selected via configuration options. The f
SUB
clock is used to provide a substitute clock for
the microcontroller just after a wake-up has occurred to enable faster wake-up times.
HIRC
Prescaler
f
H
LXT
Hi�h Speed
Oscillator
Low Speed
Oscillator
f
H
/�
f
H
/16
f
H
/64
f
H
/�
f
H
/4
f
H
/3�
HLCLK�
CKS�~CKS0
f
SYS
f
SUB
f
SUB
LIRC
HXT
f
H
Hi�h Speed Oscillator
Confi��ration Option
Low Speed Oscillator
Confi��ration Option
Fast Wake-�p from IDLE
or SLEEP Mode Control
(for HXT only )
f
SUB
IDLEN
f
TBC
f
SYS
/4
TBCK
f
TB
Time Base
WDT
f
SUB
f
TBC
Device Clock Configurations
Note: When the system clock source f
SYS
is switched to f
SUB
from f
H
, the high speed oscillator will
stop to conserve the power. Thus there is no f
H
~f
H
/64 for peripheral circuit to use.