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Table 21-2 Damping Resistance Value
Frequency (MHz)
R
(Ω)
d
Crystal Resonator: Figure 21-3 shows the equivalent circuit of the crystal resonator. Use a
crystal resonator that has the characteristics shown in table 18-3. The crystal resonator frequency
should not exceed 20 MHz.
Table 21-3 Crystal Resonator Parameters
Frequency (MHz)
R
max (Ω)
S
C
max (pF)
0
Note on Board Design: When a crystal resonator is connected, the following points should be
noted:
Other signal lines should be routed away from the oscillator circuit to prevent induction from
interfering with correct oscillation. See figure 21-4.
When designing the board, place the crystal resonator and its load capacitors as close as possible
to the XTAL and EXTAL pins.
4
500
L
XTAL
Figure 21-3 Crystal Resonator Equivalent Circuit
4
120
7
Avoid
Signal A Signal B
C
L2
C
L1
Figure 21-4 Example of Incorrect Board Design
8
12
200
0
C
L
R
s
EXTAL
AT-cut parallel-resonance type
C
0
8
12
80
60
7
7
H8S/2646 Series
XTAL
EXTAL
16
20
0
0
16
20
50
40
7
7
719
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