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Rev. 1.00, 05/04, page 457 of 544
19.1.2 External Clock Input Method
Figure 19.4 shows a typical method of connecting an external clock signal. To leave the XTAL pin
open, incidental capacitance should be 10 pF or less.
To input an inverted clock to the XTAL pin, the external clock should be set to high in standby
mode, subactive mode, subsleep mode, and watch mode. External clock input conditions are
shown in table 19.3. The frequency of the external clock should be the same as that of the system
clock (φ).
EXTAL
XTAL
External clock input
Open
(a) Example of external clock input when XTAL pin left open
EXTAL
XTAL
External clock input
(b) Example of external clock input when an inverted clock is input to XTAL pin
Figure 19.4 Example of External Clock Input