External Clock Input - Renesas H8S Series Hardware Manual

Note on Board Design: When a crystal resonator is connected, the following points should be noted.
Other signal lines should be routed away from the oscillator circuit to prevent induction from interfering with correct
oscillation. See figure 20-4.
When designing the board, place the crystal resonator and its load capacitors as close as possible to the XTAL and
EXTAL pins.
20.3.2

External Clock Input

Circuit Configuration: An external clock signal can be input as shown in the examples in figure 20-5. If the XTAL pin is
left open, make sure that stray capacitance is no more than 10 pF.
In example (b) in fugure 20-5, make sure that the external clock is held high in standby mode.
External Clock: The external clock signal should have the same frequency as the system clock (ø).
Rev.6.00 Oct.28.2004 page 664 of 1016
REJ09B0138-0600H
Avoid Signal A Signal B
C
L2
C
L1
Figure 20-4 Example of Incorrect Board Design
EXTAL
XTAL
(a) XTAL pin left open
EXTAL
XTAL
(b) Complementary clock input at XTAL pin
Figure 20-5 External Clock Input (Examples)
H8S/2357 Group
XTAL
EXTAL
External clock input
Open
External clock input