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Crystal Resonator: Figure 17.3 shows an equivalent circuit of the crystal resonator. The crystal
resonator should have the characteristics listed in table 17.2.
XTAL
Table 17.2 Crystal Resonator Parameters
Frequency (MHz)
Rs max (Ω)
Co (pF)
Use a crystal resonator with a frequency equal to the system clock frequency (φ).
Notes 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 17.4.
When the board is designed, the crystal resonator and its load capacitors should be placed as close
as possible to the XTAL and EXTAL pins.
Avoid
C
C
Figure 17.4 Oscillator Circuit Block Board Design Precautions
C
L
Figure 17.3 Crystal Resonator Equivalent Circuit
2
4
8
500
120
80
Signal A
L2
L1
L
AT-cut parallel-resonance type
C
0
10
12
70
60
7 pF max
Signal B
Rs
16
18
20
50
40
40
H8/3008
XTAL
EXTAL
EXTAL
25
TBD
431
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