R8CSLASH15 datasheet(58/277 Pages) RENESAS

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R8C/14 Group, R8C/15 Group

9. Clock Generation Circuit

Rev.2.10

Jan 19, 2006

Page 46 of 253

REJ09B0164-0210

9.2

On-Chip Oscillator Clock

This clock is supplied by an on-chip oscillator. The on-chip oscillator contains a high-speed on-chip

oscillator and a low-speed on-chip oscillator. Either an on-chip oscillator clock is selected by the HRA01

bit in the HRA0 register.

9.2.1

Low-Speed On-Chip Oscillator Clock

The clock generated by the low-speed on-chip oscillator is used as the clock source for the CPU

clock, peripheral function clock, fRING, fRING128 and fRING-S.

After reset, the on-chip oscillator clock generated by the low-speed on-chip oscillator by divide-by-8

is selected for the CPU clock.

If the main clock stops oscillating when the OCD1 to OCD0 bits in the OCD register are set to “11b”

(oscillation stop detection function enabled), the low-speed on-chip oscillator automatically starts

operating, supplying the necessary clock for the microcomputer.

The frequency of the low-speed on-chip oscillator varies depending on the supply voltage and the

operating ambient temperature. The application products must be designed with sufficient margin for

the frequency change.

9.2.2

High-Speed On-Chip Oscillator Clock

The clock generated by the high-speed on-chip oscillator is used as the clock source for the CPU

clock, peripheral function clock, fRING, fRING128, and fRING1-fast.

After reset, the on-chip oscillator clock generated by the high-speed on-chip oscillator stops. The

oscillation starts by setting the HRA00 bit in the HRA0 register to “1” (high-speed on-chip oscillator

on). The frequency can be adjusted by the HRA1 and HRA2 registers.

Since the difference in delay between the bits, adjust by changing each bit.

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