User's Manual

Table Of Contents
R01UH0823EJ0110 Rev.1.10 Page 204 of 1852
Nov 30, 2020
RX23W Group 9. Clock Generation Circuit
9.4 Sub-Clock Oscillator
The only way of supplying the clock signal from the sub-clock oscillator is connecting a crystal.
9.4.1 Connecting 32.768-kHz Crystal
To supply a clock to the sub-clock oscillator, connect a 32.768-kHz crystal, as shown in Figure 9.8.
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 XCIN and XCOUT 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 sub-clock oscillator described in Table 9.1.
Figure 9.8 Connection Example of 32.768-kHz Crystal
Figure 9.9 shows an equivalent circuit for the 32.768-kHz crystal. Use a crystal that has the characteristics listed in
Table 9.6.
Figure 9.9 Equivalent Circuit for Crystal
Table 9.6 Crystal Characteristics (Reference Values)
Frequency (kHz) 32.768 (Low CL)
R
S
max (kΩ)37
C
0
max (pF) 0.9
XCIN
XCOUT
C1
C2
C1 = 9 pF, C2 = 9 pF (reference values)
Rd
Rf
C
S
R
S
XCIN XCOUT
L
S
C
0