Datasheet

Section 6 Power-Down Modes
Rev. 1.50 Sep. 18, 2007 Page 102 of 584
REJ09B0240-0150
6.4 Direct Transition
The CPU can execute programs in two modes: active and subactive modes. A direct transition is a
transition between these two modes without stopping program execution. A direct transition can
be made by executing the SLEEP instruction while the DTON bit in SYSCR2 is set to 1. The
direct transition also enables operating frequency modification in 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 sleep or subsleep mode. Note that if a direct transition is attempted while the I bit in
CCR is set to 1, sleep or subsleep mode will be entered, and the resulting mode cannot be cleared
by means of an interrupt.
6.4.1 Direct Transition from Active Mode to Subactive Mode
The time from the start of the SLEEP instruction execution to the end of the interrupt exception
handling (the direct transition time) is calculated by equation (1).
Direct transition time = {(number of SLEEP instruction execution cycles) + (number of internal
clock cycles)}× (tcyc before transition) + (number of interrupt exception handling cycles) ×
(tsubcyc after transition) …. (1)
Example 1: Case when the CPU operating clock changes from φ
osc
to φ
w
/8
Direct transition time = (2 + 1) × t
OSC
+ 16 × 8 t
W
= 3 t
OSC
+ 128 t
W
Example 2: Case when the system clock source is Rosc/4 and the division ratio is 16; the CPU
operating clock changes from φ/16 to φ
w
/2
Direct transition time = (2 + 1) × 4 t
ROSC
× 16 + 16 × 2 t
w
= 192 t
ROSC
+ 32 t
w
[Legend]
t
OSC
: OSC clock cycle time
t
ROSC
: Period of oscillation of the on-chip oscillator
t
W
: Watch clock cycle time
t
cyc
: System clock (φ) cycle time
t
subcyc
: Subclock (φ
SUB
) cycle time