External Crystal/Ceramic Oscillator - Hxt - Holtek HT67F2350 Manual

HT67F2350/HT67F2360
HT67F2370/HT67F2390
Advanced A/D Flash MCU with LCD & EEPROM
HIRCEN
HXTEN
LXTEN
External Crystal/Ceramic Oscillator – HXT
The External Crystal/Ceramic System Oscillator is the high frequency oscillator, which is the
default oscillator clock source after power on. 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.
Note: C1 and C2 values are for guidance only.
Rev. 1.60
High Speed
FHS
Oscollators
HIRC
f
H
HXT
Low Speed
FSS
Oscollators
LXT
f
SUB
f
LIRC
LIRC
System Clock Configurations
C1
OSC1
R
P
OSC2
C2
Note: 1. R is normally not required. C1 and C2 are required.
P
2. Although not shown OSC1/OSC2 pins have a parasitic
capacitance of around 7pF.
Crystal/Resonator Oscillator
HXT Oscillator C1 and C2 Values
Crystal Frequency C1
12MHz 0 pF
8MHz 0 pF
4MHz 0 pF
1MHz 100 pF
Crystal Recommended Capacitor Values
83
f
H
f /2
H
f /4
H
f /8
H
Prescaler
f /16
H
f /32
H
f /64
H
CKS2~CKS0
f
LIRC
Internal
Oscillator
Circuit
R
F
To internal
circuits
C2
0 pF
0 pF
0 pF
100 pF
f
SYS
f
SUB
May 16, 2019