R8CSLASH15 datasheet(59/277 Pages) RENESAS

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R8C/14 Group, R8C/15 Group

9. Clock Generation Circuit

Rev.2.10

Jan 19, 2006

Page 47 of 253

REJ09B0164-0210

9.3

CPU Clock and Peripheral Function Clock

There are two type clocks: a CPU clock to operate the CPU and a peripheral function clock to operate

the peripheral functions. Refer to Figure 9.1 Clock Generation Circuit.

9.3.1

System Clock

The system clock is a clock source for the CPU and peripheral function clocks. The main clock or on-

chip oscillator clock can be selected.

9.3.2

CPU Clock

The CPU clock is an operating clock for the CPU and watchdog timer.

The system clock can be the divide-by-1 (no division), 2, 4, 8 or 16 to produce the CPU clock. Use

the CM06 bit in the CM0 register and the CM16 to CM17 bits in the CM1 register to select the value

of the division.

After reset, the low-speed on-chip oscillator clock divided-by-8 provides the CPU clock.

When entering stop mode from high-speed or medium-speed mode, the CM06 bit is set to “1”

(divide-by-8 mode).

9.3.3

Peripheral Function Clock (f1, f2, f4, f8, f32)

The peripheral function clock is operating clock for the peripheral functions.

The clock fi (i=1, 2, 4, 8, 32) is generated by the system clock divided-by-i. The clock fi is used for

timers X, Y, Z, C, serial interface and A/D converter.

When the WAIT instruction is executed after setting the CM02 bit in the CM0 register to “1”

(peripheral function clock stops in wait mode), the clock fi stops.

9.3.4

fRING and fRING128

fRING and fRING128 are operating clocks for the peripheral functions.

The fRING runs at the same frequency as the on-chip oscillator clock and can be used as the source

for the timer X. The fRING128 is generated by the fRING by dividing it by 128 and can be used for

the timer C.

When the WAIT instruction is executed, the clocks fRING and fRING128 do not stop.

9.3.5

fRING-fast

fRING-fast is used as the count source for the timer C. The fRING-fast is generated by the high-

speed on-chip oscillator and provided by setting the HRA00 bit to “1”.

When the WAIT instruction is executed, the clock fRING-fast does not stop.

9.3.6

fRING-S

fRING-S is an operating clock for the watchdog timer and voltage detection circuit. When setting the

CM14 bit to “0” (low-speed on-chip oscillator on) using the clock generated by the low-speed on-chip

oscillator, the fRING-S can be provided. When the WAIT instruction is executed or in count source

protect mode of the watchdog timer, fRING-S does not stop.

R8C/15 Datasheet(PDF) 59 Page - Renesas Technology Corp

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