Datasheet

Section 24 Clock Pulse Generator
Rev. 3.00 Mar 21, 2006 page 634 of 788
REJ09B0300-0300
24.1 Oscillator
Clock pulses can be supplied either by connecting a crystal resonator, or by providing external
clock input.
24.1.1 Connecting Crystal Resonator
Figure 24.2 shows a typical method of connecting a crystal resonator. An appropriate damping
resistance R
d
, given in table 24.1, should be used. An AT-cut parallel-resonance crystal resonator
should be used.
Figure 24.3 shows the equivalent circuit of a crystal resonator. A resonator having the
characteristics given in table 24.2 should be used.
A crystal resonator with frequency identical to that of the system clock (φ) should be used.
EXTAL
XTAL
R
d
C
L2
C
L1
C
L1
= C
L2
= 10 to 22 pF
Figure 24.2 Typical Connection to Crystal Resonator
Table 24.1 Damping Resistance Values
Frequency (MHz) 2 4 8 10 12 16 20
R
d
(Ω) 1 k 500 200 0 0 0 0
XTAL
C
L
AT-cut parallel-resonance crystal resonator
EXTAL
C
0
LR
s
Figure 24.3 Equivalent Circuit of Crystal Resonator