h8s2277 Renesas Electronics Corporation., h8s2277 Datasheet - Page 612

• Manufacturer Part Number: h8s2277
• Description: Hitachi Single-chip Microcomputer H8s/2276 Series
• Manufacturer: Renesas Electronics Corporation.

(3) Note on Switchover of External Clock
When two or more external clocks (e.g. 10 MHz and 2 MHz) are used as the system clock,
switchover of the input clock should be carried out in software standby mode.
An example of an external clock switching circuit is shown in figure 18.7, and an example of the
external clock switchover timing in figure 18.8.
590
EXTAL
Figure 18.7 Example of External Clock Switching Circuit
t
EXr
External clock 1
External clock 2
Control
circuit
Figure 18.6 External Clock Input Timing
V
CC
External interrupt signal
switchover request
switchover signal
t
EXH
0.8
External clock
External clock
t
EXf
t
EXL
Port output
External
interrupt
EXTAL
LSI
V
CC
0.2