HD404669 Datasheet, PDF (34/142 Pages) Hitachi Semiconductor – Low-Voltage AS Microcomputers with On-Chip DTMF Generation Circuit

HD404669 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. (Interrupts, timers, the serial interface, and other peripheral functions continue to
operate. The exception is the comparator, which is halted.)
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. Figure 15 shows a
flowchart of MCU operation.
Stop mode
Standby mode
Watch mode
No
RESET=1?
Yes
No
STOPC=0?
Yes
RAME=1
RESET=1? ^No
Yes
No
IF0 · IM0=1?
Yes
RAME=0
No
IF1 · IM1=1?
Yes *
IFTA ·
No
IMTA=1?
No
Yes
IF2·IM2 = 1?
Yes *
IFTC·IMTC + ^No
IF3·IM3=1?
Yes *
IFTD·IMTD + ^No
IF4·IM4=1?
Yes *
No
IFS1·IMS1=1
System clock
oscillator started
MCU reset
Yes ^*
Next instruction
execution
System clock
oscillator started
No
Next instruction
execution
IF =1,
IM=0,
IE =1?
Yes
Interrupts
enabled
Note: * Only when clearing from standby mode.
Figure 15 MCU Operation Flowchart
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