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Chapter 2 CPU Basics
II - 22
Standby Functions
2-4-3 Transition between SLOW and NORMAL
This LSI has two CPU operating modes, NORMAL and SLOW. Transition from SLOW to NORMAL requires
passing through IDLE mode.
A sample program for transition from NORMAL to SLOW mode is given below.
Program 1
MOV x'3', D0 ; Set SLOW mode.
MOV D0, (CPUM)
Transition from NORMAL to SLOW mode, when the low-frequency clock has fully stabilized, can be
done by writing to the CPU mode control register. In this case, transition through IDLE is not needed.
For transition from SLOW to NORMAL mode, the program must maintain the idle state until high-fre-
quency clock oscillation is fully stable. In IDLE mode, the CPU operates on the low-frequency clock.
For transition from SLOW to NORMAL, oscillation stabilization waiting time is required same
as that after reset. Software must count that time.
We recommend selecting the oscillation stabilization time after consulting with oscillator
manufacturers.
Sample program for transition from SLOW to NORMAL mode is given below.
Program 2
MOV x'01', D0 ; Set IDLE mode.
MOV D0, (CPUM)
Program 3
MOV x'0B', D0 ; A loop to keep approx. 6.7 ms with low-frequency clock (32 kHz)
LOOP ADD -1, D0 ; operation when changed to high-frequency clock (20 MHz).
BNE LOOP ;
SUB D0, D0 ;
MOV D0, (CPUM) ; Set NORMAL mode.