![](http://datasheet.mmic.net.cn/280000/HD4074459_datasheet_16064711/HD4074459_30.png)
HD404459 Series
30
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 since
the CPU halts.
The MCU enters standby mode when the SBY instruction is executed in active mode.
Standby mode is terminated by RESET input or an interrupt request. If it is terminated by RESET, 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. See figure 15 for the
flowchart of operation in standby mode.
Standby
Oscillator: Active
Peripheral clocks: Active
All other clocks: Stop
No
Yes
No
Yes
No
Yes
No
Yes
No
Yes
No
Yes
Yes
(SBY
only)
Watch
Oscillator: Stop
Suboscillator: Active
Peripheral clocks: Stop
All other clocks: Stop
Restart
processor clocks
Reset MCU
Execute
next instruction
Accept interrupt
Restart
processor clocks
No
Yes
RESET = 1
IF0
IM0
= 1
IF1
IM1
= 1
IFTD
IMTD
= 1
IF + IF2
IMTA
IM2
= 1
IF + IF3
IMTB
IM3
= 1
No
Yes
No
Stop
Oscillator: Stop
Suboscillator: Active/Stop
Peripheral clocks: Stop
All other clocks: Stop
RESET = 1
STOPC
= 0
RAME = 1
RAME = 0
Yes
Yes
No
No
(SBY
only)
(SBY
only)
(SBY
only)
Execute
next instruction
IF = 1,
IM = 0, and
IE = 1
*
Note:
*
The INT
interrupt
is valid only by
standby mode
cancellation.
IFWU
IMWU
= 1
IF + IFS
IMTC
IMS
= 1
Figure 15 MCU Operation Flowchart