Note On Oscillators - Renesas H8 Series Hardware Manual

8-bit single-chip microcomputer

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Section 4 Clock Pulse Generators

Note on Oscillators

Oscillator characteristics are closely related to board design and should be carefully evaluated by

the user in mask ROM and ZTAT versions, referring to the examples shown in this section.

Oscillator circuit constants will differ depending on the oscillator element, stray capacitance in its

interconnecting circuit, and other factors. Suitable constants should be determined in consultation

with the oscillator element manufacturer. Design the circuit so that the oscillator element never

receives voltages exceeding its maximum rating.

Figure 4.12 Example of Crystal and Ceramic Oscillator Element Arrangement

Figure 4.13 (1) shows an example measuring circuit with the negative resistance suggested by the

resonator manufacturer. Note that if the negative resistance of the circuit is less than that suggested

by the resonator manufacturer, it may be difficult to start the main oscillator.

If it is determined that oscillation is not occurring because the negative resistance is lower than the

level suggested by the resonator manufacturer, the circuit may be modified as shown in figure 4.13

(2) through (4). Which of the modification suggestions to use and the capacitor capacitance should

be decided based upon an evaluation of factors such as the negative resistance and the frequency

Rev. 7.00 Mar 10, 2005 page 114 of 652

REJ09B0042-0700