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R01UH0197EJ0120 Rev.1.20
Jul 21, 2011
M16C/6B Group
7. Clock Generation Circuit
7.4
Power Control
Normal operating mode, wait mode, and stop mode are provided as the power consumption control. All mode
states, except wait mode and stop mode, are called normal operating mode in this document.
7.4.1
Normal Operating Mode
Normal operating mode is further classified into seven modes.
In normal operating mode, because the CPU clock and the peripheral function clocks both are on, the CPU and
the peripheral functions are operating. Power control is exercised by controlling the CPU clock frequency. The
higher the CPU clock frequency, the greater the processing capability. The lower the CPU clock frequency, the
smaller the power consumption in the chip. If the unnecessary oscillator circuits are turned off, the power
consumption is further reduced.
Before the clock sources for the CPU clock can be switched over, the new clock source to which switched must
be oscillating stably. If the new clock source is the main clock or subclock allow a sufficient wait time in a
program until it becomes oscillating stably.
When the CPU clock source is changed from the 125 kHz on-chip oscillator to the main clock, change the
operating mode to the medium speed mode (divided by 8 mode) after the clock was divided by 8 (the CM06 bit
in the CM0 register was set to 1) in the 125 kHz on-chip oscillator mode.
7.4.1.1
High-speed Mode
The main clock divided by 1 provides the CPU clock. If the subclock is on, fC32 can be used as the count
source for timers A and B.
7.4.1.2
Medium-Speed Mode
The main clock divided by 2, 4, 8, or 16 provides the CPU clock. If the subclock is on, fC32 can be used as the
count source for timers A and B. If fOCO-S is oscillating, fOCO-S can be used as the count source for timers A
and B.
7.4.1.3
Low-Speed Mode
The subclock provides the CPU clock. The main clock is used as the clock source for the peripheral function
clock when the CM21 bit in the CM2 register is set to 0 (main clock), and the 125 kHz on-chip oscillator clock
is used when the CM21 bit is set to 1 (125 kHz on-chip oscillator clock).
The fC32 clock can be used as the count source for timers A and B.
7.4.1.4
Low Power Consumption Mode
In this mode, the main clock is turned off after being placed in low speed mode. The subclock provides the CPU
clock. The fC32 clock can be used as the count source for timers A and B. If fOCO-S is oscillating, fOCO-S can
be used as the count source for timers A and B.
Simultaneously when this mode is selected, the CM06 bit in the CM0 register becomes 1 (divided by 8 mode).
In the low power consumption mode, do not change the CM06 bit. Consequently, the medium-speed (divided
by 8) mode is to be selected when the main clock is operated next.
7.4.1.5
125 kHz On-Chip Oscillator Mode
The 125 kHz on-chip oscillator clock divided by 1 (undivided), 2, 4, 8, or 16 provides the CPU clock. The 125
kHz on-chip oscillator clock is also the clock source for the peripheral function clocks. If the subclock is on,
fC32 can be used as the count source for timers A and B. When the operating mode is returned to the high- and
medium-speed modes, set the CM06 bit in the CM0 register to 1 (divided by 8 mode).