Precautions For Power Control - Renesas M16C/60 Series Hardware Manual

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M16C/6N5 Group

1.3 Precautions for Power Control

1. When exiting stop mode by hardware reset, set RESET pin to "L" until a main clock oscillation is
stabilized.
2. Insert more than four NOP instructions after an WAIT instruction or a instruction to set the CM10 bit of
the CM1 register to "1" (all clock stopped). When shifting to wait mode or stop mode, an instruction
queue reads ahead to the next instruction to halt a program by an WAIT instruction and an instruction
to set the CM10 bit to "1". The next instruction may be executed before entering wait mode or stop
mode, depending on a combination of instruction and an execution timing.
3. Wait until the t
d(M-L)
switching the clock source for CPU clock to the main clock.
Similarly, wait until the sub clock oscillates stably before switching the clock source for CPU clock to
the sub clock.
4. Suggestions to reduce power consumption
(a) Ports
The processor retains the state of each 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 high-impedance state. When
entering wait mode or stop mode, set non-used ports to input and stabilize the potential.
(b) A-D converter
When A-D conversion is not performed, set the VCUT bit of the ADCON1 register to "0" (V
connection). When A-D conversion is performed, start the A-D conversion at least 1 µs or longer after
setting the VCUT bit to "1" (V
(c) D-A converter
When not performing D-A conversion, set the DAiE bit (i = 0, 1) of the DACON register to "0" (input
inhibited) and DAi register to "00
(d) Stopping peripheral functions
Use the CM02 bit of the CM0 register to stop the unnecessary peripheral functions during wait
mode. However, because the peripheral function clock (f
stop, this measure is not conducive to reducing the power consumption of the chip. If low speed mode
or low power dissipation mode is to be changed to wait mode, set the CM02 bit to "0" (do not peripheral
function clock stopped when in wait mode), before changing wait mode.
(e) Switching the oscillation-driving capacity
Set the driving capacity to "LOW" when oscillation is stable.
(f) External clock
When using an external clock input for the CPU clock, set the CM05 bit of the CM0 register to "1"
(stop). Setting the CM05 bit to "1" disables the X
amount of current drawn in the chip. (When using an external clock input, note that the clock remains
fed into the chip regardless of how the CM05 bit is set.)
Rev.1.00 2003.05.30 page 3
elapses or main clock oscillation stabilization time, whichever is longer, before
connection).
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16
1.3 Precautions for Power Control
____________
) generated from the sub clock does not
C32
pin from functioning, which helps to reduce the
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