Datasheet

Section 25 Clock Pulse Generator
Rev. 2.00 Sep. 28, 2009 Page 834 of 994
REJ09B0452-0200
25.1 Oscillator
Clock pulses can be supplied either by connecting a crystal resonator or by providing external
clock input.
25.1.1 Connecting Crystal Resonator
Figure 25.2 shows a typical method for connecting a crystal resonator. An appropriate damping
resistance R
d
, given in table 25.1 should be used. An AT-cut parallel-resonance crystal resonator
should be used.
Figure 25.3 shows an equivalent circuit of a crystal resonator. A crystal resonator having the
characteristics given in table 25.2 should be used.
The frequency of the crystal resonator should be the same as that of the system clock (φ).
EXTAL
XTAL
R
d
C
L2
C
L1
C
L1
= C
L2
= 10 to 22 pF
Figure 25.2 Typical Connection to Crystal Resonator
Table 25.1 Damping Resistor Values
Frequency (MHz) 8 10 12 16 20
R
d
(Ω) 200 0 0 0 0
XTAL
C
L
AT-cut parallel-resonance crystal resonato
r
EXTAL
C
0
LR
s
Figure 25.3 Equivalent Circuit of Crystal Resonator