Externa� Cr�Sta�/Ceramic Osci - Holtek HT68F Series Manual

HT68F20/HT68F30/HT68F40/HT68F50/HT68F60
HT68FU30/HT68FU40/HT68FU50/HT68FU60
Enhanced I/O Flash Type 8-Bit MCU with EEPROM
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
thatthe crystal and any associated resistors andcapacitors along with interconnectinglines are all
located as close to the MCUas possible.
Crystal Frequency
Note: C1 and C2 va��es are for g�idance on��.
Rev. 2.10
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
Crystal Oscillator C1 and C2 Values
C1
12MHz 0pF
8 MHz 0pF
� MHz 0pF
1 MHz 100pF
Crystal Recommended Capacitor Values
51
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
C2
0pF
0pF
0pF
100pF
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