Rev. 1.00, 09/03, page 615 of 704
21.2.2
External Clock Input Method
Figure 21.4 shows a typical method of connecting an external clock signal. To leave the XTAL pin
open, parasitic 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. External clock input conditions are shown in table 21.3.
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 21.4 Example of External Clock Input
Table 21.3 External Clock Input Conditions
VCC = 3.0 to 3.6 V
Item
Symbol Min.
Max.
Unit Test
Conditions
External clock input
pulse width low level
t
EXL
15
ns
External clock input
pulse width high level
t
EXH
15
ns
External clock rising
time
t
EXr
5 ns
External clock falling
time
t
EXf
5 ns
Figure 21.5
Clock pulse width low
level
t
CL
0.4 0.6 t
cyc
Clock pulse width high
level
t
CH
0.4 0.6 t
cyc
Figure 24.3
Содержание H8S/2437
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