R01UH0823EJ0100 Rev.1.00 Page 196 of 1823
Jul 31, 2019
RX23W Group 9. Clock Generation Circuit
9.3 Main Clock Oscillator
There are two ways of supplying the clock signal from the main clock oscillator: connecting an oscillator or the input of
an external clock signal.
9.3.1 Connecting a Crystal
Figure 9.4 shows an example of connecting a crystal.
A damping resistor (Rd) should be added, if necessary. Since the resistor values vary depending on the resonator and the
oscillation drive capability, use values recommended by the resonator manufacturer. If use of an external feedback
resistor (Rf) is directed by the resonator manufacturer, insert an Rf between EXTAL and XTAL by following the
instruction.
When connecting a resonator to supply the clock, the frequency of the resonator should be in the frequency range of the
resonator for the main clock oscillator described in
Table 9.1.
Figure 9.4 Example of Crystal Connection
Figure 9.5 shows an equivalent circuit of the crystal. Use a crystal that has the characteristics shown in Table 9.5 as a
reference.
Figure 9.5 Equivalent Circuit of Crystal
Table 9.4 Damping Resistance (Reference Values)
Frequency (MHz) 2 8 16 20
Rd (Ω) 0000
Table 9.5 Crystal Characteristics (Reference Values)
Frequency (MHz) 8 12 16
R
S
max (Ω) 200 120 56
C
0
max (pF) 1.3 1.3 1.4
EXTAL
XTAL
C
L1
C
L2
R
d
C
L1
= C
L2
= 3 to 7 pF (reference value)
R
f
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