Hitachi H8/3937 Series Hardware Manual page 102

3. External clock input
Connect the external clock to the DX
DX
1
DX
2
Figure 4-10 Pin Connection when Inputting External Clock
Frequency
Duty
90
pin and leave the DX
1
Open
Subclock (øw)
45% to 55%
pin open, as shown in figure 4-10.
2
External clock input