Datasheet

Section 21 Clock Pulse Generator
Rev. 3.00 Mar 17, 2006 page 815 of 926
REJ09B0283-0300
Table 21.2 Crystal Resonator Characteristics
Frequency (MHz) 8 12 16 20 25
R
S
max (Ω) 8060504040
C
0
max (pF) 77777
21.2.2 External Clock Input
An external clock signal can be input as shown in the examples in figure 21.4. If the XTAL pin is
left open, make sure that parasitic capacitance is no more than 10 pF. When the counter clock is
input to the XTAL pin, make sure that the external clock is held high in standby mode.
Table 21.3 shows the input conditions for the external clock. When an external clock is used, the
range of its frequencies is from 8 to 25 MHz.
EXTAL
XTAL
External clock input
Open
(a) XTAL pin left open
EXTAL
XTAL
External clock input
(b) Counter clock input at XTAL pin
Figure 21.4 External Clock Input (Examples)