Rev. 1.50
4�
����st ��� �01�
Rev. 1.50
43
����st ��� �01�
HT66F0175/HT66F0185
A/D Flash MCU with EEPROM
HT66F0175/HT66F0185
A/D Flash MCU with EEPROM
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 )
System Clock Configurations
External Crystal/Ceramic Oscillator – HXT
The External Crystal/Ceramic System Oscillator is one of the high frequency oscillator choices,
which is selected via configuration option. For most crystal oscillator configurations, the simple
connection of a crystal across OSC1 and OSC2 will create the necessary phase shift and feedback for
oscillation, without requiring external capacitors. However, for some crystal types and frequencies,
to ensure oscillation, it may be necessary to add two small value capacitors, C1 and C2. Using a
ceramic resonator will usually require two small value capacitors, C1 and C2, to be connected as
shown for oscillation to occur. The values of C1 and C2 should be selected in consultation with the
crystal or resonator manufacturer’s specification.
For oscillator stability and to minimise the effects of noise and crosstalk, it is important to ensure
that the crystal and any associated resistors and capacitors along with interconnecting lines are all
located as close to the MCU as possible.
Crystal/Resonator Oscillator
HXT Oscillator C1 and C2 Values
Crystal Frequency
C1
C2
1�MHz
0 pF
0 pF
�MHz
0 pF
0 pF
4MHz
0 pF
0 pF
1MHz
100 pF
100 pF
Note: C1 and C� val�es are for ��idance only.
Crystal Recommended Capacitor Values