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22.6
Software Standby Mode
22.6.1
Software Standby Mode
A transition is made to software standby mode when the SLEEP instruction is executed when the
SBYCR SSBY bit = 1 and the LPWRCR LSON bit = 0, and the TCSR (WDT1) PSS bit = 0. In
this mode, the CPU, on-chip supporting modules, and oscillator all stop. However, the contents of
the CPU's internal registers, RAM data, and the states of on-chip supporting modules other than
the SCI, A/D converter, Motor control PWM, HCAN and I/O ports, are retained. Whether the
address bus and bus control signals are placed in the high-impedance state.
In this mode the oscillator stops, and therefore power dissipation is significantly reduced.
22.6.2
Clearing Software Standby Mode
Software standby mode is cleared by an external interrupt (NMI pin, or pins IRQ0 to IRQ5), or by
means of the RES pin or STBY pin.
• Clearing with an interrupt
When an NMI or IRQ0 to IRQ5 interrupt request signal is input, clock oscillation starts, and
after the elapse of the time set in bits STS2 to STS0 in SYSCR, stable clocks are supplied to
the entire H8S/2646 Series chip, software standby mode is cleared, and interrupt exception
handling is started.
When clearing software standby mode with an IRQ0 to IRQ5 interrupt, set the corresponding
enable bit to 1 and ensure that no interrupt with a higher priority than interrupts IRQ0 to IRQ5
is generated. Software standby mode cannot be cleared if the interrupt has been masked on the
CPU side or has been designated as a DTC activation source.
• Clearing with the RES pin
When the RES pin is driven low, clock oscillation is started. At the same time as clock
oscillation starts, clocks are supplied to the entire H8S/2646 Series chip. Note that the RES
pin must be held low until clock oscillation stabilizes. When the RES pin goes high, the CPU
begins reset exception handling.
• Clearing with the STBY pin
When the STBY pin is driven low, a transition is made to hardware standby mode.
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