1.8 Precautions for Power Control
22
Mitsubishi microcomputers
M16C / 62P Group
SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER
development
Preliminary Specifications Rev.1.0
Specifications in this manual are tentative and subject to change.
1.8 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
CM1 register to
“
1
”
. 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
”
(all
clocks stopped). The next instruction may be executed before entering wait mode or stop mode, de-
pending on a combination of instruction and an execution timing.
3. Wait until the t
su(M-L)
elapses or main clock oscillation stabilization time, whichever is longer, before
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 ADiCON1 register to
“
0
”
(no V
REF
connec-
tion). When A-D conversion is performed, start the A-D conversion at least 1
μ
s or longer after setting
the VCUT bit to
“
1
”
(V
REF
connection).
(c) D-A converter
When not performing D-A conversion, set the DAi bit (i=0, 1) of DACON register to
“
0
”
(input inhibited)
and DAi register to
“
00
16
”
.
(d) Stopping peripheral functions
Use the CM0 register CM02 bit to stop the unnecessary peripheral functions during wait mode. How-
ever, because the peripheral function clock (f
C32
) generated from the sub-clock does not stop, this
measure is not conducive to reducing the power consumption of the chip. During low speed mode and
low power dissipation mode, do not set the CM02 bit to
“
1
”
(peripheral function clock stopped when in
wait mode) before entering 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 CM0 register CM05 bit to
“
1
”
(stop).
Setting the CM05 bit to
“
1
”
disables the X
OUT
pin from functioning, which helps to reduce the 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.)