M30218 Datasheet, PDF (393/467 Pages) Mitsubishi Electric Semiconductor – M30218 Group

Power Control
Mitsubishi microcomputers
M30218 Group
SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER
2.14.4 Precautions in Power Control
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(1) When returning from stop mode by hardware reset, RESET pin must be set to “L” level until
main clock oscillation is stabilized.
(2) When switching to either wait mode or stop mode, instructions occupying four bytes either
from the WAIT instruction or from the instruction that sets the every-clock stop bit to “1” within
the instruction queue are prefetched and then the program stops. So put at least four NOPs
in succession either to the WAIT instruction or to the instruction that sets the every-clock stop
bit to 1.
(3) Before the count source for BCLK can be changed from XIN to XCIN or vice versa, the clock to
which the count source is going to be switched must be oscillating stably. Allow a wait time in
software for the oscillation to stabilize before switching over the clock.
(4) Suggestions to reduce power consumption
• Ports
The processor retains the state of each programmable I/O port even when it goes to
wait mode or to stop mode. A current flows in active I/O ports. A pass current flows in
input ports that float. When entering wait mode or stop mode, set non-used ports to
input and stabilize the potential.
(a) A-D converter
A current always flows in the VREF pin. When entering wait mode or stop mode, set
the Vref connection bit to “0” so that no current flows into the VREF pin.
(b) D-A converter
The processor retains the D-A state even when entering wait mode or stop mode.
Disable the output from the D-A converter then work on the programmable I/O ports.
(c) Stopping peripheral functions
In wait mode, stop non-used wait peripheral functions using the peripheral function
clock stop bit.
(d) Switching the oscillation-driving capacity
Set the driving capacity to “LOW” when oscillation is stable.
(e) External clock
When using an external clock input for the CPU clock, set the main clock stop bit to
“1”. Setting the main clock stop bit to “1” causes the XOUT pin not to operate and the
power consumption goes down (when using an external clock input, the clock signal
is input regardless of the content of the main clock stop bit).
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