M16C6S_09 Datasheet, PDF (36/208 Pages) Renesas Technology Corp – SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER

M16C/6S Group
Clock Generation Circuit
Power Control
There are three power control modes. For convenience’ sake, all modes other than wait and stop modes
are referred to as normal operation mode here.
(1) Normal Operation Mode
Normal operation mode is further classified into three modes.
In normal operation 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, allow a sufficient wait time in a
program until it becomes oscillating stably.
Where the CPU clock source is changed from the On-chip Oscillator to the main clock, change the opera-
tion mode to the medium speed mode (divided by 8 mode) after the clock was divided by 8 (the CM06 bit
of CM0 register was set to “1”) in the On-chip Oscillator mode.
• High-speed Mode
The main clock divided by 1 provides the CPU clock.
• Medium-speed Mode
The main clock divided by 2, 4, 8 or 16 provides the CPU clock.
• On-chip Oscillator Mode
The On-chip Oscillator clock divided by 1 (undivided), 2, 4, 8 or 16 provides the CPU clock. The On-
chip Oscillator clock is also the clock source for the peripheral function clocks.
Rev.5.01 Dec 10, 2009 page 36 of 201
REJ03B0014-0501