HD404849 Datasheet, PDF (31/125 Pages) Hitachi Semiconductor – 4-Bit Single-Chip Microcomputer

HD404849 Series
Active Mode: All MCU functions operate according to the clock generated by the system oscillator 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.
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