95
6.9
Direct Transition
The CPU can execute programs in two modes: active and subactive mode. A direct transition is a
transition between these two modes without stopping program execution. A direct transition can
be made by executing a SLEEP instruction while the DTON bit in SYSCR2 is set to 1. The direct
transition also enables operating frequency modification in the active or subactive mode. After the
mode transition, direct transition interrupt exception handling starts.
If the direct transition interrupt is disabled in interrupt enable register 1, a transition is made
instead to the sleep or subsleep mode. Note that if a direct transition is attempted while the I bit in
CCR is set to 1, the sleep or subsleep mode will be entered, and the resulting mode cannot be
cleared by means of an interrupt.
•
Direct transition from the active mode to the subactive mode
When a SLEEP instruction is executed in the active mode while the DTON and LSON bits in
SYSCR2 are set to 1, a transition is made to the subactive mode.
•
Direct transition from the subactive mode to the active mode
When a SLEEP instruction is executed in the subactive mode while the DTON bit in SYSCR2
is set to 1 and the LSON bit in SYSCR2 is cleared to 0, a direct transition is made to the active
mode after the waiting time set in SYSCR1 bits STS2 to STS0 has elapsed.
6.9.1
Direct Transition Time
•
Direct transition from the active mode to the subactive mode
When a SLEEP instruction is executed in the active mode while the DTON and LSON bits in
SYSCR2 are set to 1, a transition is made to the subactive mode. The time from the start of
SLEEP instruction execution to the end of interrupt exception handling (the direct transition
time) is calculated by equation (1).
Direct transition time = {(number of SLEEP instruction execution states) + (number of internal
processing states)}
×
(tcyc before transition) + (number of interrupt exception handling states)
×
(tsubcyc after transition) .............................................................................................. (1)
[Example]
Direct transition time = (2 + 1)
×
tosc + 14
×
8tw = 3tosc + 112tw
(when the CPU operating clock of øosc
→
øw/8 is selected)
<Symbols>
tosc: OSC clock cycle time
tw: watch clock cycle time
tcyc: system clock (ø) cycle time
tsubcyc: subclock (øSUB) cycle time
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