Datasheet

Section 20 Clock Pulse Generator
Rev.6.00 Sep. 27, 2007 Page 915 of 1268
REJ09B0220-0600
Crystal Resonator: Figure 20.3 shows the equivalent circuit of the crystal resonator. Use a crystal
resonator that has the characteristics shown in table 20.3 and the same resonance frequency as the
system clock (φ).
XTAL
C
L
AT-cut parallel-resonance type
EXTAL
C
0
LR
s
Figure 20.3 Crystal Resonator Equivalent Circuit
Table 20.3 Crystal Resonator Characteristics
Frequency (MHz) 2 4 8 12 16 20 25
R
S
max (Ω) 500 120 80 60 50 40 40
C
0
max (pF) 7 7 7 7 7 7 7
Notes on Board Design: When a crystal resonator is connected, the following points should be
noted:
Other signal lines should be routed away from the oscillator circuit to prevent induction from
interfering with correct oscillation. See figure 20.4.
When designing the board, place the crystal resonator and its load capacitors as close as possible
to the XTAL and EXTAL pins.
C
L2
Signal A Signal B
C
L1
Chip
XTAL
EXTAL
A
void
Figure 20.4 Example of Incorrect Board Design