E202075_HD404889 Datasheet, PDF (57/202 Pages) Renesas Technology Corp – Low-Voltage AS Microcomputers with On-Chip LCD Circuit

HD404889/HD404899/HD404878/HD404868 Series
Stop mode:
In stop mode, all MCU function stop except that states prior to entry into stop mode are retained. This
mode thus has the lowest power consumption of all operating mode.
In stop mode, the OSC₁ and OSC₂ oscillators stop. Bit 3 (SSR3) of the system clock select register (SSR:
$004) (figure 24) can be used to select the active (= 0) or stopped (= 1) state for the X1 and X2 oscillators.
The MCU is switched to stop mode by executing a STOP instruction while bit 3 (TMA3) of timer mode
register A (TMA: $00F) is cleared to 0 in active mode. Stop mode is cleared by RESET or WU₀ to WU₃
input. When stop mode is cleared by RESET, the RESET signal should be input for at least the oscillation
settling time (tRC) (see "AC Characteristics") shown in figure 15. Then, the MCU is initialized and starts
instruction execution from the start (address 0) of the program.
When the MCU detects a falling edge at WU₀ to WU₃ in stop mode, it automatically waits for the
oscillation settling time, then switches to active mode. After the transition to active mode, the MCU
resumes program execution from the instruction following the STOP instruction.
If stop mode is cleared by wakeup input, RAM data and registers retain their values prior to entering stop
mode.
Oscillator
Stop mode
Internal clock
RESET
STOP instruction executed
tres
(At least oscillation settling time (tRC))
Figure 15 Timing Chart for Clearing Stop Mode by RESET Input
Note: If stop mode is cleared by wakeup input when an external clock is used as the system clock
(OSC1), the subclock should not be stopped in stop mode.
Watch mode:
In watch mode, the realtime clock function (timer A) and LCD function using the X1 and X2 oscillators
operate, but other functions stop. This mode thus has the second lowest power consumption after stop
mode, and is useful for performing realtime clock display only.
In watch mode, the OSC₁ and OSC₂ oscillators stop but the X1 and X2 oscillators continue to operate.
The MCU is switched to watch mode by executing a STOP instruction while TMA3 = 1 in active mode, or
by executing a STOP/SBY instruction in subactive mode.
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