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CHAPTER 3 CPU
I
Gear Function (Function for Switching the Speed of the Main Clock)
Four different main clock speeds can be selected by writing "00
B
" to "11
B
" into the main clock
speed select bits (SYCC: CS1, CS0) of the system clock control register.
CPU and each peripheral circuit operate at the switched main clock speed. However, the
timebase timer and watch prescaler are not affected by the gear function.
By reducing the main clock speed, power consumption can be reduced.
I
Operation in Main Clock Mode
In normal operation in main clock mode (main RUN mode), both the main clock and subclock
oscillate. The watch prescaler is operated by the subclock, whereas CPU, the timebase timer,
and other peripheral circuits are operated by the main clock.
The speed of the main clock can be switched to a value other than that of the timebase timer
during operation in main clock mode (gear function). A transition to the main sleep mode or
main stop mode is enabled by specifying the standby mode.
Operation always starts in main RUN mode regardless of the type of reset that occurs (release
by the reset in each operation mode).
H
Transition from the main clock mode to the subclock mode
A transition from the main clock mode to the subclock mode is caused by writing "0" into the
system clock select bit (SYCC: SCS) of the system clock control register.
The current operating clock can be checked by reading the system clock monitor bit (SYCC:
SCM) of the system clock control register.
To make a transition to the subclock mode, for example, just after power-on, it is necessary to
wait at least the subclock oscillation stabilization wait time created by the watch prescaler using
software before making a transition.