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21.2
Oscillator
Clock pulses can be supplied either by connecting a crystal resonator or by providing external
clock input.
21.2.1
Connecting Crystal Resonator
Figure 21.2 shows a typical method of connecting a crystal resonator. An appropriate damping
resistance R
, given in table 21.1, should be used. An AT-cut parallel-resonance crystal resonator
d
should be used.
Figure 21.3 shows the equivalent circuit of a crystal resonator. A crystal resonator having the
characteristics given in table 21.2 should be used.
Figure 21.2 Typical Connection to Crystal Resonator
Table 21.1 Damping Resistor Values
Frequency (MHz)
R
(Ω)
d
XTAL
Table 21.2 Crystal Resonator Parameters
Frequency(MHz)
R
(max.) (Ω)
S
C
(max.) (pF)
0
Rev. 1.00, 09/03, page 614 of 704
EXTAL
XTAL
R
d
10
12
0
0
C
L
L
C
0
Figure 21.3 Equivalent Circuit of Crystal Resonator
10
12
70
60
7
7
C
L1
C
C
= C
L2
L1
L2
16
20
0
0
R
s
EXTAL
AT-cut parallel-resonance crystal resonator
16
20
50
40
7
7
= 10 to 22 pF
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