Inputting An External Clock; Figure 21.4 External Clock Input (Examples); Table 21.3 External Clock Input Conditions - Hitachi H8S/2215 Series Hardware Manual

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.
Table 21.3 shows the input conditions for the external clock.

Table 21.3 External Clock Input Conditions

Item
External clock input low pulse width
External clock input high pulse width
External clock rise time
External clock fall time
Clock low pulse width level
Clock high pulse width level
Rev. 3.0, 10/02, page 600 of 686
EXTAL
XTAL
(a) XTAL pin left open
EXTAL
XTAL
(b) Complementary clock input at XTAL pin

Figure 21.4 External Clock Input (Examples)

Symbol
t
EXL
t
EXH
t
EXr
t
EXf
t
CL
t
CH
External clock input
Open
External clock input
VCC = 2.7V – 3.6 V
Min Max
25 —
25 —
— 6.25
— 6.25
0.4 0.6
0.4 0.6
Test
Unit Conditions
ns Figure 21.5
ns
ns
ns
tcyc Figure 24.2
tcyc