R8C13 datasheet(46/224 Pages) RENESAS

46 / 224 page

Rev.1.20

Jan 27, 2006

page 35 of 205

REJ09B0111-0120

R8C/13 Group

6.2 On-Chip Oscillator Clock

This clock is supplied by a on-chip oscillator. There are two kinds of on-chip oscillator: high-speed on-

chip oscillator and low-speed on-chip oscillator. These oscillators are selected by the bit HR01 bit in

the HR0 register.

6.2.1 Low-Speed On-Chip Oscillator Clock

The clock derived from 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 derived from low-speed on-chip oscillator by divided 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 “112” (oscil-

lation stop detection function enabled), the low-speed on-chip oscillator automatically starts operat-

ing, supplying the necessary clock for the microcomputer.

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

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

the frequency change.

6.2.2 High-Speed On-Chip Oscillator Clock

The clock derived from 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 derived from high-speed on-chip oscillator is halted. The

oscillation is started by setting the HR00 bit in the HR0 register to “1” (high-speed on-chip oscillator

on). The frequency can be adjusted by the HR1 register.

The relationship between the value of HR1 register and the period of high-speed on-chip oscillator is

shown below. It is noted that the difference in delay between the bits should be adjusted by changing

each bit. Bit 7 should be set be “0”.

Period of high-speed on-chip oscillator = td(HR offset) + (64 ✕ b6 + 32 ✕ b5 + 16 ✕ b4 + 8 ✕ b3 + 4

✕ b2 + 2 ✕ b1 + b0) ✕ td(HR)

b0 to b6 : Bits in HR1 register

6.2 On-chip Oscillator Clock

R8C13 Datasheet(PDF) 46 Page - Renesas Technology Corp