Datasheet

Section 24 Clock Pulse Generator
Rev. 4.00 Sep 27, 2006 page 734 of 1130
REJ09B0327-0400
24.3 Oscillator
Clock pulses can be supplied by connecting a crystal resonator, or by input of an external clock.
24.3.1 Connecting a Crystal Resonator
Circuit Configuration
A crystal resonator can be connected as shown in the example in figure 24.2. Select the damping
resistance R
d
according to table 24.2. 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
Figure 24.2 Connection of Crystal Resonator (Example)
Table 24.2 Damping Resistance Value
Frequency (MHz) 2 4 8 10 12 16 20
R
d
(Ω
ΩΩ
Ω) 1k 500 200 0 0 0 0
Crystal resonator
Figure 24.3 shows the equivalent circuit of the crystal resonator. Use a crystal resonator that has
the characteristics shown in table 24.3 and the same frequency as the system clock (φ).
XTAL
C
L
AT-cut parallel-resonance type
EXTAL
C
0
LR
s
Figure 24.3 Crystal Resonator Equivalent Circuit