Rev. 1.0, 09/02, page 470 of 568
20.2 Oscillator
Clock pulses can be supplied by connecting a crystal resonator, or by input of an external clock. In
either case, the input clock should not exceed 20 MHz.
20.2.1
Connecting a Crystal Resonator
Circuit Configuration: A crystal resonator can be connected as shown in the example in figure
20.2. Select the damping resistance R
d
according to table 20.1. An AT-cut parallel-resonance
crystal should be used.
EXTAL
XTAL
R
d
C
L2
C
L1
C
L1
= C
L2
= 10 to 22 pF
Figure 20.2 Connection of Crystal Resonator (Example)
Table 20.1 Damping Resistance Value
Frequency
(MHz) 4 8 12 16 20 24
R
d
(
Ω
)
500
200
0 0 0 0
Figure 20.3 shows the equivalent circuit of the crystal resonator. Use a crystal resonator that has
the characteristics shown in table 20.2.
XTAL
C
L
AT-cut parallel-resonance type
EXTAL
C
0
L
R
s
Figure 20.3 Crystal Resonator Equivalent Circuit
Table 20.2 Crystal Resonator Characteristics
Frequency
(MHz) 4 8 12 16 20 24
R
S
max (
Ω
)
120
80 60 50 40 40
C
0
max
(pF)
7 7 7 7 7 7
Summary of Contents for H8S/2627
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