R8C2H Datasheet, PDF (298/367 Pages) Renesas Technology Corp – MCU

R8C/2H Group, R8C/2J Group
21. Reducing Power Consumption
21. Reducing Power Consumption
21.1 Overview
This chapter describes key points and processing methods for reducing power consumption.
21.2 Key Points and Processing Methods for Reducing Power Consumption
Key points for reducing power consumption are shown below. They should be referred to when designing a system
or creating a program.
21.2.1 Voltage Detection Circuit
When voltage monitor 1 and comparator 1 are not used, set the VCA26 bit in the VCA2 register to 0 (voltage
detection 1 circuit disabled). When voltage monitor 2 and comparator 2 are not used, set the VCA27 bit in the
VCA2 register to 0 (voltage detection 2 circuit disabled).
If the power-on reset and voltage monitor 0 reset are not used, set the VCA25 bit in the VCA2 register to 0
(voltage detection 0 circuit disabled).
21.2.2 Ports
Even after the MCU enters wait mode or stop mode, the states of the I/O ports are retained. Current flows into
the output ports in the active state, and shoot-through current flows into the input ports in the high-impedance
state. Unnecessary ports should be set to input and fixed to a stable electric potential before the MCU enters
wait mode or stop mode.
21.2.3 Clocks
Power consumption generally depends on the number of the operating clocks and their frequencies. The fewer
the number of operating clocks or the lower their frequencies, the more power consumption decreases.
Unnecessary clocks should be stopped accordingly.
Stopping low-speed on-chip oscillator oscillation: CM14 bit in CM1 register (for R8C/2H Group only)
Stopping high-speed on-chip oscillator oscillation: HRA00 bit in HRA0 register
21.2.4 Selecting Oscillation Drive Capacity (for R8C/2H Group only)
Set the drive capacity of the XCIN clock oscillation circuit to “LOW”. Confirm that the circuit oscillates stably
while it is in the “LOW” state.
Selecting XCIN-XCOUT drive capacity: CM03 bit in CM0 register
21.2.5 Wait Mode, Stop Mode
Power consumption can be reduced in wait mode and stop mode. Refer to 11.4 Power Control for details.
21.2.6 Stopping Peripheral Function Clocks
If the peripheral function f1, f2, f4, f8, and f32 clocks are not necessary in wait mode, set the CM02 bit in the
CM0 register to 1 (peripheral function clock stops in wait mode). This will stop the f1, f2, f4, f8, and f32 clocks
in wait mode.
21.2.7 Timers
If timer RA is not used, set the TCKCUT bit in the TRAMR register to 1 (count source cutoff).
If timer RB is not used, set the TCKCUT bit in the TRBMR register to 1 (count source cutoff).
Rev.1.00 Mar 28, 2008 Page 278 of 341
REJ09B0388-0100