M16CSLASH1N datasheet(40/238 Pages) RENESAS

40 / 238 page

Rev.1.00

Oct 20, 2004

page 28 of 222

M16C/1N Group

6. Clock Generation Circuit

REJ09B0007-0100Z

The following describes the clocks generated by the clock generation circuit.

6.1 Main Clock

The main clock is generated by the main clock oscillation circuit. After reset, oscillation starts. The clock

can be stopped using the main clock stop bit (bit 5 at address 000616). Stopping the clock reduces the

power dissipation.

After the oscillation of the main clock oscillation circuit has stabilized, the drive capacity of the XOUT pin

can be reduced using the XIN-XOUT drive capacity select bit (bit 5 at address 000716). Reducing the drive

capacity of the XOUT pin reduces the power dissipation. This bit changes to "1" when shifting from high-

speed/medium-speed mode to stop mode and at a reset. When shifting from low-speed/low power dissi-

pation mode to stop mode, the value before stop mode is retained.

Figure 6.5 shows the examples of main clock connection circuit.

XIN

XOUT

Externally derived clock

Open

Vcc

Vss

Microcomputer

(Built-in feedback resistor)

XIN

XOUT

CIN

COUT

(Note 1)

Microcomputer

(Built-in feedback resistor)

External ceramic oscillator

External clock input

Note 1: Insert a damping resistor if required. The resistance will vary depending on the oscillator and the oscillation

drive capacity setting. Use the value recommended by the maker of the oscillator.

When the oscillation drive capacity is set to low, check that oscillation is stable. Also, if the oscillator

manufacturer’s data sheet specifies that a feedback resistor be added external to the chip, insert a feedback

resistor between XIN and XOUT following the instruction.

Figure 6.6 Examples of main clock connection circuit

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