R8C/13 Group
6.4 Power Control
6.4 Power Control
There are three power control modes. All modes other than wait and stop modes are referred to as
normal operation mode.
6.4.1 Normal Operation Mode
Normal operation mode is further classified into four 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.
• High-speed Mode
The main clock divided by 1 (undivided) provides the CPU clock. If the CM14 bit is set to “0” (low-
speed on-chip oscillator on) or the HR00 bit in the HR0 register is set to “1” (high-speed on-chip
oscillator on), the fRING and fRING128 can be used for timers Y and C. When the HR00 bit is set to “1”,
fRING-fast can be used for timer C.
• Medium-speed Mode
The main clock divided by 2, 4, 8 or 16 provides the CPU clock. If the CM14 bit is set to “0” (low-
speed on-chip oscillator on) or the HR00 bit in the HR0 register is set to “1” (high-speed on-chip
oscillator on), the fRING and fRING128 can be used for timers Y and C. When the HR00 bit is set to “1”,
fRING-fast can be used for timer C.
• High-speed, Low-speed, 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. When the HR00 bit is
set to “1”, fRING-fast can be used for timer C.
Rev.1.20 Jan 27, 2006 page 37 of 205
REJ09B0111-0120
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