Rev. 3.0, 10/02, page 600 of 686
21.2.2
Inputting an External Clock
An external clock signal can be input as shown in an example in figure 21.4. If the XTAL pin is
left open, make sure that stray capacitance is no more than 10 pF. When complementary clock
input to XTAL pin, the external clock input should be fixed high in standby mode.
EXTAL
XTAL
EXTAL
XTAL
External clock input
Open
External clock input
(a) XTAL pin left open
(b) Complementary clock input at XTAL pin
Figure 21.4 External Clock Input (Examples)
Table 21.3 shows the input conditions for the external clock.
Table 21.3
External Clock Input Conditions
VCC = 2.7V – 3.6 V
Item
Symbol
Min
Max
Unit
Test
Conditions
External clock input low pulse width
t
EXL
25
—
ns
External clock input high pulse width
t
EXH
25
—
ns
External clock rise time
t
EXr
—
6.25
ns
External clock fall time
t
EXf
—
6.25
ns
Figure 21.5
Clock low pulse width level
t
CL
0.4
0.6
tcyc
Figure 24.2
Clock high pulse width level
t
CH
0.4
0.6
tcyc
Summary of Contents for H8S/2215 Series
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