Datasheet

Section 19 Clock Pulse Generator
Rev.7.00 Dec. 24, 2008 Page 600 of 698
REJ09B0074-0700
19.2 System Clock Oscillator
Clock pulses can be supplied by connecting a crystal resonator, or by input of an external clock.
19.2.1 Connecting a Crystal Resonator
A crystal resonator can be connected as shown in the example in figure 19.2. Select the damping
resistance R
d
according to table 19.1. 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
(Recommended value, including
stray capacitance of circuit board)
Figure 19.2 Connection of Crystal Resonator (Example)
Table 19.1 Damping Resistance Value
Frequency (MHz) 6 8 10 13 16 20 24
R
d
(Ω) 300 200 100 0 0 0 0
Figure 19.3 shows the equivalent circuit of the crystal resonator. Use a crystal resonator that has
the characteristics shown in table 19.2.
XTAL
C
L
AT-cut parallel-resonance type
EXTAL
C
0
LR
s
Figure 19.3 Crystal Resonator Equivalent Circuit
Table 19.2 Crystal Resonator Characteristics
Frequency (MHz) 6 8 10 13 16 20 24
R
S
max (Ω) 100 80 60 60 50 40 40
C
0
max (pF) 7 7 7 7 7 7 7