3069RF-ZTAT Datasheet, PDF (710/1003 Pages) Renesas Technology Corp – RENESAS 16-BIT SINGLE-CHIP MICROCOMPUTER

19.2 Oscillator Circuit
Clock pulses can be supplied by connecting a crystal resonator, or by input of an external clock
signal.
19.2.1 Connecting a Crystal Resonator
Circuit Configuration: A crystal resonator can be connected as in the example in figure 19.2.
Damping resistance Rd should be selected according to table 19.1 (1), and external capacitances
C_L1 and C_L2 according to table 19.1 (2). An AT-cut parallel-resonance crystal should be used.
C_L1
EXTAL
XTAL
Rd
C_L2
Figure 19.2 Connection of Crystal Resonator (Example)
If a crystal resonator with a frequency higher than 20 MHz is connected, the external load
capacitance values in table 19.1 (2) should not exceed 10 pF. Also, in order to improve the
accuracy of the oscillation frequency, a thorough study of oscillation matching evaluation, etc.,
should be carried out when deciding the circuit constants.
Table 19.1 (1) Damping Resistance Value
Damping
Resistance
Value
10 ≤ f ≤ 13
Frequency f (MHz)
13 < f ≤ 16
16 < f ≤ 18
18 < f ≤ 25
Rd (Ω)
0
0
0
0
Note: A crystal resonator between 10 MHz and 25 MHz can be used. If the chip is to be
operated at less than 10 MHz, the on-chip frequency divider should be used. (A crystal
resonator of less than 10 MHz cannot be used.)
Table 19.1 (2) External Capacitance Values
External Capacitance Value
C_L1 = C_L2 (pF)
Frequency f (MHz)
20 < f ≤ 25
10
10 ≤ f ≤ 20
10 to 22
Rev. 5.0, 09/04, page 688 of 978