H83847R Datasheet, PDF (162/719 Pages) Renesas Technology Corp – Renesas 8-Bit Single-Chip Microcomputer H8 Family/H8/300L Super Low Power Series

Section 4 Clock Pulse Generators
4.5 Note on Oscillators
Oscillator characteristics are closely related to board design and should be carefully evaluated by
the user in mask ROM, ZTAT™ and F-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.
TEST
OSC1
OSC2
Vss
X2
X1
P17
(Vss)
Figure 4.10 Example of Crystal and Ceramic Oscillator Element Arrangement
Figure 4.11 (1) shows an example measuring circuit with the negative resistance suggested by the
oscillator manufacturer. Note that if the negative resistance of the circuit is less than that suggested
by the oscillator 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 oscillator manufacturer, the circuit may be modified as shown in figure 4.11
(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
deviation.
Rev. 6.00 Aug 04, 2006 page 126 of 680
REJ09B0145-0600