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21.3
Duty Adjustment Circuit
The duty adjustment circuit is valid when the oscillation frequency is more than 5 MHz. This
circuit adjusts the duty of the clock output by the oscillator and inputs it to the divider.
21.4
Divider
The divider divides the clock output by the duty adjustment circuit, and generates the system clock
(φ) of 1/1, 1/2, and 1/4.
21.5
Usage Notes
21.5.1
Note on Resonator
Since all kinds of characteristics of the resonator are closely related to the board design by the
user, use the example of resonator connection in this document for only reference; be sure to use
an resonator that has been sufficiently evaluated by the user. Consult with the resonator
manufacturer about the resonator circuit ratings which vary depending on the stray capacitances of
the resonator and installation circuit. Make sure the voltage applied to the oscillation pins do not
exceed the maximum rating.
21.5.2
Notes on Board Design
When using a crystal resonator, the crystal resonator and its load capacitors should be placed as
close as possible to the EXTAL and XTAL pins. Other signal lines should be routed away from
the oscillation circuit to prevent inductive interference with the correct oscillation as shown in
figure 21.7.
Figure 21.7 Note on Board Design of Oscillation Circuit Section
Prohibited
Signal A Signal B
C
L2
C
L1
This LSI
XTAL
EXTAL
Rev. 1.00, 09/03, page 617 of 704
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