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M16C/28 Group
Under development Preliminary specification
Specifications in this manual are tentative and subject to change.
7. Clock Generation Circuit
Rev.0.60 2004.02.01
page 42 of N
REJ09B0047-0060Z
7.5 CPU Clock and Peripheral Function Clock
The CPU clock is used to operate the CPU and peripheral function clocks are used to operate the periph-
eral functions.
7.5.1 CPU Clock
This is the operating clock for the CPU and watchdog timer.
The clock source for the CPU clock can be chosen to be the main clock, sub clock, ring oscillator clock or
the PLL clock.
If the main clock or ring oscillator clock is selected as the clock source for the CPU clock, the selected
clock source can be divided by 1 (undivided), 2, 4, 8 or 16 to produce the CPU clock. Use the CM06 bit in
CM0 register and the CM17 to CM16 bits in CM1 register to select the divide-by-n value.
When the PLL clock is selected as the clock source for the CPU clock, the CM06 bit should be set to “0”
and the CM17 to CM16 bits to “002” (undivided).
After reset, the ring oscillator clock divided by 16 provides the CPU clock.
Note that when entering stop mode from high or middle speed mode, ring oscillator mode or ring oscillator
low power dissipation mode, or when the CM05 bit of CM0 register is set to “1” (main clock turned off) in
low-speed mode, the CM06 bit of CM0 register is set to “1” (divide-by-8 mode).
7.5.2 Peripheral Function Clock(f1, f2, f8, f32, f1SIO, f2SIO, f8SIO, f32SIO, fAD, fC32)
These are operating clocks for the peripheral functions.
Of these, fi (i = 1, 2, 8, 32) and fiSIO are derived from the main clock, PLL clock or ring oscillator clock by
dividing them by i. The clock fi is used for timers A and B, and fiSIO is used for serial I/O.
The fAD clock is produced from the main clock, PLL clock or ring oscillator clock, and is used for the A-D
converter.
When the WAIT instruction is executed after setting the CM02 bit of CM0 register to “1” (peripheral
function clock turned off during wait mode), or when the microcomputer is in low power dissipation mode,
the fi, fiSIO and fAD clocks are turned off.
The fC32 clock is produced from the sub clock, and is used for timers A and B. This clock can only be used
when the sub clock is on.