HD64F2168 Datasheet, PDF (762/874 Pages) Renesas Technology Corp – Renesas 16-Bit Single-Chip Microcomputer

22.1 Oscillator
Clock pulses can be supplied either by connecting a crystal resonator or by providing external
clock input.
22.1.1 Connecting Crystal Resonator
Figure 22.2 shows a typical method of connecting a crystal resonator. An appropriate damping
resistance R_d, given in table 22.1, should be used. An AT-cut parallel-resonance crystal resonator
should be used.
Figure 22.3 shows the equivalent circuit of a crystal resonator. A crystal resonator having the
characteristics given in table 22.2 should be used.
When PFSEL is high, the system clock (φ) frequency should be no more than 25 MHz and a
crystal resonator with frequency identical to that of the system clock (φ) should be used. When
PFSEL is low, a crystal resonator with ¼ times the frequency of the system clock (φ) should be
used.
C_L1
EXTAL
XTAL
R_d
C_L2
C_L1 = C_L2 = 10 to 22 pF
Figure 22.2 Typical Connection to Crystal Resonator
Table 22.1 Damping Resistance Values
Frequency (MHz)
5
8
10
12
16
20
25
R_d (Ω)
300
200
0
0
0
0
0
XTAL
C_L
L
R_s
EXTAL
C₀
AT-cut parallel-resonance crystal resonator
Figure 22.3 Equivalent Circuit of Crystal Resonator
Rev. 3.00, 03/04, page 722 of 830