HD404639R Datasheet, PDF (30/135 Pages) Renesas Technology Corp – 4-Bit Single-Chip Microcomputer

HD404639R Series
Active Mode: All MCU functions operate according to the clock generated by the system oscillators OSC₁
and OSC₂.
Standby Mode: In standby mode, the oscillators continue to operate, but the clocks related to instruction
execution stop. Therefore, the CPU operation stops, but all RAM and register contents are retained, and the
D or R port status, when set to output, is maintained. Peripheral functions such as interrupts, timers, and
serial interface continue to operate. The power dissipation in this mode is lower than in active mode
because the CPU stops.
The MCU enters standby mode when the SBY instruction is executed in active mode.
Standby mode is terminated by a RESET input or an interrupt request. If it is terminated by RESET input,
the MCU is reset as well. After an interrupt request, the MCU enters active mode and executes the next
instruction after the SBY instruction. If the interrupt enable flag is 1, the interrupt is then processed; if it is
0, the interrupt request is left pending and normal instruction execution continues. A flowchart of
operation in standby mode is shown in figure 15.
Stop Mode: In stop mode, all MCU operations stop and RAM data is retained. Therefore, the power
dissipation in this mode is the least of all modes. The OSC₁ and OSC₂ oscillator stops. For the X1 and X2
oscillator to operate or stop can be selected by setting bit 3 of system clock select register 1 (SSR1: $029;
operating: SSR13 = 0, stop: SSR13 = 1) (figure 24). The MCU enters stop mode if the STOP instruction is
executed in active mode when bit 3 of timer mode register A (TMA: $008) is set to 0 (TMA3 = 0) (figure
41).
Stop mode is terminated by a RESET input or a STOPC input as shown in figure 16. RESET or STOPC
must be applied for at least one t_RC to stabilize oscillation (refer to the AC Characteristics section). When
the MCU restarts after stop mode is cancelled, all RAM contents before entering stop mode are retained,
but the accuracy of the contents of the accumulator, B register, W register, X/SPX register, Y/SPY register,
carry flag, and serial data register cannot be guaranteed.
Watch Mode: In watch mode, the clock function (timer A) using the X1 and X2 oscillator operates but
other function operations stop. Therefore, the power dissipation in this mode is the second least to stop
mode, and this mode is convenient when only clock display is used. In this mode, the OSC₁ and OSC₂
oscillator stops, but the X1 and X2 oscillator operates. The MCU enters watch mode if the STOP
instruction is executed in active mode when TMA3 = 1, or if the STOP or SBY instruction is executed in
subactive mode.
Watch mode is terminated by a RESET input or a timer-A/INT₀ interrupt request. For details of RESET
input, refer to the Stop Mode section. When terminated by a timer-A/INT₀ interrupt request, the MCU
enters active mode if LSON is 0, or subactive mode if LSON is 1. After an interrupt request is generated,
the time required to enter active mode is t_RC for a timer A interrupt, and T_X (where T + t_RC < T_X < 2T + t_RC)
for an INT₀ interrupt, as shown in figures 17 and 18.
Operation during mode transition is the same as that at standby mode cancellation (figure 15).
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