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16.2 Oscillator Circuit
Clock pulses can be supplied by connecting a crystal resonator, or by input of an external clock
signal.
16.2.1 Connecting a Crystal Resonator
Circuit Configuration: A crystal resonator can be connected as in the example in figure 16-2.
The damping resistance Rd should be selected according to table 16-1. An AT-cut parallel-
resonance crystal should be used.
Figure 16-2 Connection of Crystal Resonator (Example)
Table 16-1 Damping Resistance Value (Example)
Frequency (MHz)
Rd (Ω)
Crystal Resonator: Figure 16-3 shows an equivalent circuit of the crystal resonator. The crystal
resonator should have the characteristics listed in table 16-2.
XTAL
EXTAL
XTAL
Rd
2
4
1 k
500
L
Figure 16-3 Crystal Resonator Equivalent Circuit
C
L1
C
C
L2
8
10
200
0
C
L
C
O
= C
= 10 pF to 22 pF
L1
L2
12
16
0
0
Rs
AT-cut parallel-resonance type
18
0
EXTAL
487
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