Exte�Nal C�Ystal/Ce�A�Ic Oscillato� - Hxt - Holtek HT66F488 Manual

High Speed Oscillators
HXT
HIRC
Low Speed Oscillators
LXT
LIRC
Note: The OSC1/XT1 and OSC2/XT2 share the same pins, so the HXT oscillator and the LXT
oscillator can not be selected at the same time.
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.
Rev. 1.21
f
H
6-stage Prescaler
High Speed Oscillator
Configuration Option
f
H
f /32
H
f /64
H
f
L
Low Speed Oscillator
Configuration Option
System Clock Configurations
C 1
O S C 1
R p
O S C 2
C 2
N o t e : 1 . R p i s n o r m a l l y n o t r e q u i r e d . C 1 a n d C 2 a r e r e q u i r e d .
2 . A l t h o u g h n o t s h o w n O S C 1 / O S C 2 p i n s h a v e a p a r a s i t i c
c a p a c i t a n c e o f a r o u n d 7 p F .
Crystal/Resonator Oscillator – HXT
36
HT66F488/HT66F489
A/D Flash MCU with EEPROM
f /2
H
f /4
H
f /8
H
/16
f
L
HLCLK,
CKS2~CKS0 bits
f
SUB
Fast Wake-up from SLEEP Mode or
IDLE Mode Control (for HXT only)
I n t e r n a l
O s c i l l a t o r
C i r c u i t
R f
T o i n t e r n a l
c i r c u i t s
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f
SYS