M16C28 Datasheet, PDF (75/423 Pages) Renesas Technology Corp – 16-BIT SINGLE-CHIP MICROCOMPUTER M16C FAMILY / M16C/Tiny SERIES

M16C/28 Group (M16C/28, M16C/28B)
7. Clock Generation Circuit
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, on-chip oscillator clock
or the PLL clock.
If the main clock or on-chip 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 on-chip oscillator clock divided by 16 provides the CPU clock.
Note that when entering stop mode from high or middle speed mode, on-chip oscillator mode or on-chip
oscillator low power dissipation mode, or when the CM05 bit in the CM0 register is set to “1” (main clock
turned off) in low-speed mode, the CM06 bit in the 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 on-chip oscillator clock
by dividing them by i. The clock fi is used for Timer A, Timer B, SI/O3 and SI/O4 while fiSIO is used for
UART0 to UART2. Additionally, the f1 and f2 clocks are also used for dead time timer, Timer S, multi-
master I²C bus.
The fAD clock is produced from the main clock, PLL clock or on-chip oscillator clock, and is used for the A/
D converter.
When the WAIT instruction is executed after setting the CM02 bit in the 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.
Rev. 2.00 Jan. 31, 2007 ^{page 55} of 385
REJ09B0047-0200