R8C/36T-A Group
10. Power Control
Under development Preliminary document
Specifications in this document are tentative and subject to change.
R01UH0240EJ0010 Rev.0.10
Page 114 of 728
Aug 05, 2011
10.3.1
High-Speed Clock Mode
When the CM13 bit in the CM1 register is 1 (XIN-XOUT pin) and bits CM42 to CM40 in the CM4 register are
000b, the XIN clock is used as the system clock, and the CPU clock is obtained by dividing the system clock by
1 (no division), 2, 4, 8, or 16.
10.3.2
Low-Speed Clock Mode
When bits CM42 to CM40 in the CM4 register are 010b, the XCIN clock is used as the system clock, and the
CPU clock is obtained by dividing the system clock by 1 (no division), 2, 4, 8, or 16.
In this mode, low-power operation can be achieved by stopping the XIN clock and the high-speed on-chip
oscillator and setting the FMR27 bit in the FMR2 register to 1 (low-current-consumption read mode enabled).
Furthermore, if the MCU enters wait mode from this mode, current consumption in wait mode can be reduced
even further by setting the SVD0 bit in the SVDC register to 1 (transition to low-power-consumption mode
enabled).
10.3.3
High-Speed On-Chip Oscillator Mode
When the FRA00 bit is 1 (high-speed on-chip oscillator on) and bits CM42 to CM40 in the CM4 register are
101b, the high-speed on-chip oscillator is used as the system clock. At this time, the CPU clock is obtained by
dividing the system clock by 1 (no division), 2, 4, 8, or 16.
10.3.4
Low-Speed On-Chip Oscillator Mode
When the CM14 bit is 0 (low-speed on-chip oscillator on) and bits CM42 to CM40 are 001b, the low-speed on-
chip oscillator is used as the system clock. At this time, the CPU clock is obtained by dividing the system clock
by 1 (no division), 2, 4, 8, or 16.
In this mode, low-power operation can be enabled by stopping the XIN clock and the high-speed on-chip
oscillator and setting the FMR27 bit to 1 (low-current-consumption read mode enabled). Low-power-
consumption mode can be used when the CPU clock is the low-speed on-chip oscillator divided by 4, 8 or 16.
When the CPU clock is the low-speed on-chip oscillator divided by 1 (no division) or 2, do not use low-power-
consumption mode. Set the FMR27 bit to 1 after setting the division ratio for the CPU clock.
Furthermore, if the MCU enters wait mode from this mode, current consumption in wait mode can be reduced
even further by setting the SVD0 bit to 1 (transition to low-power-consumption mode enabled).