HD404654 Series
25
Table 17 I/O Status in Low-Power Dissipation Modes
Output
Input
Standby Mode
Stop Mode
Active Mode
D
0
–D
9
D
12
–D
13
, RD
0
, RD
1
, RE
0
R0–R4
Retained
High impedance
Input enabled
—
—
Input enabled
Retained or output of
peripheral functions
High impedance
Input enabled
Reset by
RESET
input or
by watchdog timer
f
OSC
:
CPU
:
:
Oscillate
Stop
f
cyc
f
OSC
:
CPU
:
PER
:
Oscillate
f
cyc
f
cyc
f
OSC
:
CPU
:
PER
:
Standby mode
(TMA3 = 0)
SBY
Interrupt
f
OSC
:
f
cyc
:
Main oscillation
frequency
f /4 or or f /32
(hardware selectable)
System clock
Clock for other
peripheral functions
Active
mode
CPU
:
PER
:
RESET1
RESET2
RAME = 0
RAME = 1
STOPC
STOP
Stop
Stop
Stop
Stop mode
Figure 11 MCU Status Transitions
Active Mode:
All MCU functions operate according to the clock generated by the system oscillators OSC
1
and OSC
2
.
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 12.