Rev. 1.0, 09/02, page 485 of 568
21.4
Software Standby Mode
21.4.1
Transition to Software Standby Mode
A transition is made to software standby mode if the SLEEP instruction is executed when the
SBYCR SSBY bit is set to 1. In this mode, the CPU, on-chip peripheral modules, and oscillator,
all stop. However, the contents of the CPU’s internal registers, on-chip RAM data, and the states
of on-chip peripheral modules other than the SCI, A/D converter, and the states of I/O ports, are
retained. In this mode, the oscillator stops, and therefore power consumption is significantly
reduced.
21.4.2
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 time set in bits STS0 to STS2 in SBYCR has elapsed, stable clocks are supplied to the
entire 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 chip. Note that the
RES
pin must be held low
until clock oscillation settles. 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.
Summary of Contents for H8S/2627
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