20.4 Software Standby Mode
20.4.1 Transition to Software Standby Mode
To enter software standby mode, execute the SLEEP instruction while the SSBY bit is set to 1 in
SYSCR.
In software standby mode, current dissipation is reduced to an extremely low level because the
CPU, clock, and on-chip supporting modules all halt. The DMAC and on-chip supporting modules
are reset. As long as the specified voltage is supplied, however, CPU register contents and on-chip
RAM data are retained. The settings of the I/O ports and refresh controller* are also held.
Note: * RTCNT and bits 7 and 6 of RTMCSR are initialized. Other bits and registers hold their
previous states.
20.4.2 Exit from Software Standby Mode
Software standby mode can be exited by input of an external interrupt at the NMI, IRQ
0
, IRQ
1
, or
IRQ
2
pin, or by input at the
RES
or
STBY
pin.
Exit by Interrupt: When an NMI, IRQ
0
, IRQ
1
, or IRQ
2
interrupt request signal is received, the
clock oscillator begins operating. After the oscillator settling time selected by bits STS2 to STS0
in SYSCR, stable clock signals are supplied to the entire chip, software standby mode ends, and
interrupt exception handling begins. Software standby mode is not exited if the interrupt enable
bits of interrupts IRQ
0
, IRQ
1
, and IRQ
2
are cleared to 0, or if these interrupts are masked in the
CPU.
Exit by
RES
Input: When the
RES
input goes low, the clock oscillator starts and clock pulses are
supplied immediately to the entire chip. The
RES
signal must be held low long enough for the
clock oscillator to stabilize. When
RES
goes high, the CPU starts reset exception handling.
Exit by
STBY
Input: Low input at the
STBY
pin causes a transition to hardware standby mode.
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