3.5 Low Power Consumption Modes
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In clock mode, the contents of dedicated registers (such as accumulators) and internal RAM are
retained.
q Wake-up from Watch Mode
The standby control circuit is used for wake-up from watch mode at input of a reset signal or an
interrupt request. If watch mode is released by a reset source, the MB90660A will be in reset state when
it wakes up from clock mode.
For wake-up from watch mode, the standby control circuit will first release watch mode before moving
into PLL clock oscillation stabilization wait state. Because the MCS bit is not cleared by an external
reset signal, any instance in which the reset interval is shorter than the PLL clock oscillation
stabilization wait period will result in the main clock being used for the reset sequence. Note also that in
such instances the timebase timer is not cleared during the PLL clock oscillation stabilization wait
period, and therefore the wait period may vary from 213 to 3*213 main clock cycles.
In watch mode, the occurrence of any interrupt request stronger (higher) than level 7 in a peripheral
circuit will cause a wake-up from watch mode through the standby control circuit. After wake-up, the
same processing is applied as for a normal interrupt. If the interrupt is accepted according to the values
of the I flag, ILM bit and interrupt control register (ICR), the CPU will execute interrupt processing. If
the interrupt is not accepted, execution will continue with the next instruction following the instruction
that caused the transition to watch mode.
[CAUTION]
When interrupt processing is executed, the normal procedure is to first execute the
instruction following the instruction that caused the transition to sleep mode before
branching to interrupt processing.
[CAUTION]
Upon wake-up from watch mode, the MB90660A will transition into PLL clock
oscillation stabilization wait state, so that when the PLL clock is not in use, the MCS bit
should be overwritten with the value ‘1’ by the next instruction immediately after the reset
or interrupt designation.
(3) Stop Mode
q Transition to Stop Mode
The standby control circuit initiates transition to stop mode when the value ‘1’ is written to the STP bit
in the low-power consumption mode control register while the MCS bit in the clock control register is
set to ‘1.’ In stop mode, the source oscillation is stopped, stopping all MB90660A chip functions. This
is therefore the mode with the lowest-power consumption in which data is retained.
Also, the SPL bit in the LPMCR register can be used to determine whether I/O pins are placed in high-
impedance state or retain their values immediately preceding the transition to stop mode.
If an interrupt request is generated at the time that ‘1’ is written to the STP bit, the standby control
circuit will not make the transition to stop mode.