430
17.2
Oscillator Circuit
Clock pulses can be supplied by connecting a crystal resonator, or by input of an external clock
signal.
17.2.1
Connecting a Crystal Resonator
Circuit Configuration: A crystal resonator can be connected as in the example in figure 17.2.
Damping resistance Rd should be selected according to table 17.1 (1), and external capacitances
C
L1
and C
L2
according to table 17.1 (2). An AT-cut parallel-resonance crystal should be used.
EXTAL
XTAL
C
L1
C
L2
Rd
Figure 17.2 Connection of Crystal Resonator (Example)
If a crystal resonator with a frequency higher than 20 MHz is connected, the external load
capacitance values in table 17.1 (2) should not exceed 10 [pF]. Also, in order to improve the
accuracy of the oscillation frequency, a thorough study of oscillation matching evaluation, etc.,
should be carried out when deciding the circuit constants.
Table 17.1 (1) Damping Resistance Value
Damping
Resistance
Frequency f (MHz)
Value
2
2
<
f
≤
4 4
<
f
≤
8 8
<
f
≤
10 10
<
f
≤
13 13
<
f
≤
16 16
<
f
≤
18 18
<
f
≤
25
Rd (
Ω
)
1 k
500
200
0
0
0
0
0
Note:
A crystal resonator between 2 MHz and 25 MHz can be used. If the chip is to be operated
at less than 2 MHz, the on-chip frequency divider should be used. (A crystal resonator of
less than 2 MHz cannot be used.)
Table 17.1 (2) External Capacitance Values
External Capacitance Value
5 V Version
Low-Voltage Version
Frequency f (MHz)
20
<
f
≤
25
2
≤
f
≤
20
2
≤
f
≤
13
2
≤
f
≤
TBD
C
L1
= C
L2
(pF)
10
10 to 22
10 to 22
10
Summary of Contents for H8/3008
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