HD404654 Datasheet, PDF (27/111 Pages) Hitachi Semiconductor – 4-Bit Single-Chip Microcomputer

Table 17 I/O Status in Low-Power Dissipation Modes
D₀–D₉
D₁₂–D₁₃, RD₀, RD₁, RE₀
R0–R4
Output
Standby Mode
Retained
—
Retained or output of
peripheral functions
Stop Mode
High impedance
—
High impedance
HD404654 Series
Input
Active Mode
Input enabled
Input enabled
Input enabled
Reset by
RESET input or
by watchdog timer
f_OSC: Main oscillation
frequency
f_cyc: f_OSC/4 or or f_OSC/32
(hardware selectable)
ø _CPU: _{System clock}
ø_PER: Clock for other
peripheral functions
Standby mode
RAME = 0
RAME = 1
RESET1 RESET2
Active
mode
STOPC
f_OSC:
ø _CPU:
ø _PER:
Oscillate
Stop
f_cyc
SBY
Interrupt
f_OSC:
ø _CPU:
ø _PER:
Oscillate
f_cyc
f_cyc
STOP
Stop mode
(TMA3 = 0)
f_OSC:
ø _CPU:
ø _PER:
Stop
Stop
Stop
Figure 11 MCU Status Transitions
Active Mode: All MCU functions operate according to the clock generated by the system oscillators 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 12.
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