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20.2
Oscillator Circuit
Clock pulses can be supplied by connecting a crystal resonator, or by input of an external clock
signal.
20.2.1
Connecting a Crystal Resonator
Circuit Configuration: A crystal resonator can be connected as in the example in figure 20.2.
Damping resistance Rd should be selected according to table 20.1 (1), and external capacitances
C
and C
according to table 20.1 (2). An AT-cut parallel-resonance crystal should be used.
L1
L2
Figure 20.2 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 20.1 (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 20.1 (1) Damping Resistance Value
Damping
Resistance
Value
2 < < < < f ≤ ≤ ≤ ≤ 4 4 < < < < f ≤ ≤ ≤ ≤ 8 8 < < < < f ≤ ≤ ≤ ≤ 10 10 < < < < f ≤ ≤ ≤ ≤ 13 13 < < < < f ≤ ≤ ≤ ≤ 16 16 < < < < f ≤ ≤ ≤ ≤ 18 18 < < < < f ≤ ≤ ≤ ≤ 25
2
Rd (Ω)
1 k
500
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 20.1 (2) External Capacitance Values
External Capacitance Value
Frequency f (MHz)
C
= C
(pF)
L1
L2
Note: * Conditions for the H8/3064F-ZTAT B-mask version and H8/3062F-ZTAT B-mask version.
628
EXTAL
XTAL
Rd
Frequency f (MHz)
200
0
5 V Version
20 < < < < f ≤ ≤ ≤ ≤ 25
10
C
L1
C
L2
0
0
2 ≤ ≤ ≤ ≤ f ≤ ≤ ≤ ≤ 20
10 to 22
0
0
Low-Voltage Version
2 ≤ ≤ ≤ ≤ f ≤ ≤ ≤ ≤ 13
10 to 22
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