M16C User Manual.pdf

Power ControlMitsubishi microcomputersM16C / 62 GroupSINGLE-CHIP 16-BIT CMOS MICROCOMPUTER2.14 Power Control2.14.1 Overview‘Power Control’ refers to the reduction of CPU power consumption by stopping the CPU and oscillators,or decreasing the operation clock. The following is a description of the three available power controlmodes:(1) ModesPower control is available in three modes.(a) Normal operation mode• High-speed modeDivide-by-1 frequency of the main clock becomes the BCLK. The CPU operates with the BCLKselected. Each peripheral function operates according to its assigned clock.• Medium-speed modeDivide-by-2, divide-by-4, divide-by-8, or divide-by-16 frequency of the main clock becomes theBCLK. The CPU operates according to the BCLK selected. Each peripheral function operatesaccording to its assigned clock.• Low-speed modefc becomes the BCLK. The CPU operates according to the fc clock. The fc clock is supplied by thesecondary clock. Each peripheral function operates according to its assigned clock.• Low power consumption modeThe main clock operating in low-speed mode is stopped. The CPU operates according to the fcclock. The fc clock is supplied by the secondary clock. The only peripheral functions that operateare those with the sub-clock selected as the count source.(b) Wait modeThe CPU operation is stopped. The oscillators do not stop.(c) Stop modeAll oscillators stop. The CPU and all built-in peripheral functions stop. This mode, among the threemodes listed here, is the most effective in decreasing power consumption.Figure 2.14.1 is the state transition diagram of the above modes.(2) Switching the driving capacity of the oscillation circuitBoth the main clock and the secondary clock have the ability to switch the driving capacity. Reducingthe driving capacity after the oscillation stabilizes allows for further reduction in power consumption.438