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Section 25 Clock Pulse Generator
25.1
Oscillator
Clock pulses can be supplied either by connecting a crystal resonator or by providing external
clock input.
25.1.1
Connecting Crystal Resonator
Figure 25.2 shows a typical method for connecting a crystal resonator. An appropriate damping
resistance R
, given in table 25.1 should be used. An AT-cut parallel-resonance crystal resonator
d
should be used.
Figure 25.3 shows an equivalent circuit of a crystal resonator. A crystal resonator having the
characteristics given in table 25.2 should be used.
The frequency of the crystal resonator should be the same as that of the system clock (φ).
Figure 25.2 Typical Connection to Crystal Resonator
Table 25.1 Damping Resistor Values
Frequency (MHz)
R
(Ω)
d
XTAL
Rev. 1.00 May 09, 2008 Page 802 of 954
REJ09B0462-0100
EXTAL
XTAL
R
d
8
10
200
0
C
L
L
C
0
Figure 25.3 Equivalent Circuit of Crystal Resonator
C
L1
C
C
= C
L2
L1
L2
12
16
0
0
R
s
EXTAL
AT-cut parallel-resonance crystal resonator
= 10 to 22 pF
20
0
25
0
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