H8SLASH3028F datasheet(656/923 Pages) RENESAS

656 / 923 page

Rev. 2.00, 09/03, page 626 of 890

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

CL1 and CL2 according to table 19.1 (2). An AT-cut parallel-resonance crystal should be used.

EXTAL

XTAL

CL1

CL2

Figure 19.2 Connection of Crystal Resonator (Example)

If a crystal resonator with a frequency higher than 16 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

Frequency f (MHz)

Damping

Resistance

Value

< f ≤ 44 < f ≤ 88 < f ≤ 10 10 < f ≤ 13 13 < f ≤ 16 16 < f ≤ 18 18 < f ≤ 25

Rd (

Ω)

1 k

500

200

Note: A crystal resonator between 2 MHz and 25 MHz can be used. If the chip is to be operated

at less than 2 MHz, the on-chip frequency divider should be used. (A crystal resonator of

less than 2 MHz cannot be used.)

Table 19.1 (2)

External Capacitance Values

External Capacitance Value

3.3 V Version

Frequency f (MHz)

≤ f ≤ 16

< f ≤ 25

CL1 = CL2 (pF)

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