Rev. 1.00
42
September 11, 2018
Rev. 1.00
43
September 11, 2018
HT45F4050
A/D NFC Flash MCU
HT45F4050
A/D NFC Flash MCU
HXTEN
LXTEN
HIRCEN
HXT
Prescaler
f
H
LXT
High Speed
Oscillators
Low Speed
Oscillators
f
H
/2
f
H
/16
f
H
/64
f
H
/8
f
H
/4
f
H
/32
CKS2~CKS0
f
SYS
f
SUB
f
SUB
FSS
LIRC
f
LIRC
f
LIRC
HIRC
f
H
FHS
IDLE0
SLEEP
IDLE2
SLEEP
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 a software control bit, FHS. 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: 1. R
P
is normally not required. C1 and C2 are required.
2. Although not shown OSC1/OSC2 pins have a parasitic
capacitance of around 7pF.
To internal
circuits
Internal
Oscillator
Circuit
C1
C2
OSC1
OSC2
R
F
R
P
Crystal/Resonator Oscillator – HXT