M16CSLASH1N datasheet(216/238 Pages) RENESAS

216 / 238 page

Rev.1.00

Oct 20, 2004

page 204 of 222

M16C/1N Group

REJ090007-0100Z

20. Precautionary Notes in Using the Device

20.1 Clock

20.1.1 External Clock

Do not stop the external clock when it is connected to the XIN pin and the main clock is selected as the

CPU clock.

20.1.2 Power Control

____________

When exiting stop mode by hardware reset, set RESET pin to "L" for at least 200 µs or longer.

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". 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, depending on a combination of instruction and an execution timing.

3. In the main clock oscillation or low power dissipation mode, set the CM02 bit of the CM0 register to

"0" (do not stop peripheral function clock in wait mode).

4. Wait until the td(M-L) elapses or main clock oscillation stabilization time, whichever is longer, be-

fore 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.

5. Suggestions to reduce power consumption

• 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-imped-

ance state. When entering wait mode or stop mode, set non-used ports to input and stabilize

the potential.

• A/D converter

When A/D conversion is not performed, set the VCUT bit of the ADCON1 register to "0" (VREF

not 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" (VREF connection).

• D/A converter

When not performing D/A conversion, set the DAE bit of the DACON register to "0" (input

inhibited) and DA register to "0016".

• Switching the oscillation-driving capacity

Set the driving capacity to "LOW" when oscillation is stable.

• 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 XOUT 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.)

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