HD404459 Datasheet, PDF (32/122 Pages) Renesas Technology Corp – 4-bit HMCS400-series microcomputers

HD404459 Series
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.
Stop
Standby
Oscillator: Stop
Suboscillator: Active/Stop
Peripheral clocks: Stop
All other clocks: Stop
Oscillator: Active
Peripheral clocks: Active
All other clocks: Stop
Watch
Oscillator: Stop
Suboscillator: Active
Peripheral clocks: Stop
All other clocks: Stop
No
RESET = 1?
Yes
No
STOPC = 0?
Yes
RAME = 1
No
RESET = 1?
Yes
No
IF0 • IM0 = 1?
RAME = 0
Yes
No
IF1 • IM1 = 1?
Yes _{IFTD • IMTD No}
= 1?
Yes
IFTA •
IMTA + IF2 •
No
IM2 = 1?
Yes^* IFTB •
IMTB + IF3 •
No
IM3 = 1?
Yes
IFTC •
IMTC + IFS •
No
IMS = 1?
(SBY
only)
(SBY
only)
(SBY
only)
(SBY
only)
Yes _{IFWU • IMWU No}
= 1?
Yes
Restart
processor clocks
Execute
next instruction
Restart
processor clocks
Reset MCU
No
IF = 1,
IM = 0, and
IE = 1?
Yes
Execute
next instruction
Accept interrupt
Figure 15 MCU Operation Flowchart
Note: * The INT₂ interrupt
is valid only by
standby mode
cancellation.
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