Panasonic MN101C77C - Manual (Page 72)

Chapter 2 CPU Basics
II - 20 Standby Functions
„ HALT Modes (HALT0, HALT1)
−
The CPU stops operating. But both of the oscillators remain operational in HALT0 and only the high-
frequency oscillator stops operating in HALT1.
−
An interrupt returns the CPU to the previous CPU operating mode that is, to NORMAL from HALT0 or
to SLOW from HALT1.
„ STOP Modes (STOP0, STOP1)
−
The CPU and both of the oscillators stop operating.
−
An interrupt restarts the oscillators and, after allowing time for them to stabilize, returns the CPU to the
previous CPU operating mode - that is, to NORMAL from STOP0 or to SLOW from STOP1.
„ SLOW Mode
−
This mode executes the software using the low-frequency clock. Since the high-frequency oscillator is
turned off, the device consumes less power while executing the software.
„ IDLE Mode
−
This mode allows time for the high-frequency oscillator to stabilize when the software is changing from
SLOW to NORMAL mode.
To reduce power dissipation in STOP and HALT modes, it is necessary to check the stability of both the
output current from pins and port level of input pins. For output pins, the output level should match the
external level or direction control should be changed to input mode. For input pins, the external level
should be fixed.
This LSI has two system clock oscillation circuits. OSC is for high-frequency operation (NORMAL mode)
and XI is for low-frequency operation (SLOW mode). Transition between NORMAL and SLOW modes or
to standby mode is controlled by the CPU mode control register (CPUM). Reset and interrupts are the
return factors from standby mode. A wait period is inserted for oscillation stabilization at reset and when
returning from STOP mode, but not when returning from HALT mode. High/low-frequency oscillation
mode is automatically returned to the same state as existed before entering standby mode.
To stabilize the synchronization at the moment of switching clock speed between high speed
oscillation (fosc) and low speed oscillation (fx), fosc should be set to 2.5 times or higher
frequency than fx.