R8C2K datasheet(100/471 Pages) RENESAS

100 / 471 page

R8C/2K Group, R8C/2L Group

10. Clock Generation Circuit

Rev.1.10

Dec 21, 2007

Page 83 of 450

REJ09B0406-0110

10.3

CPU Clock and Peripheral Function Clock

There are a CPU clock to operate the CPU and a peripheral function clock to operate the peripheral functions. Refer

to Figure 10.1 Clock Generation Circuit.

10.3.1

System Clock

The system clock is the clock source for the CPU and peripheral function clocks. Either the XIN clock or the

on-chip oscillator clock can be selected.

10.3.2

CPU Clock

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

The system clock can be divided by 1 (no division), 2, 4, 8, or 16 to produce the CPU clock. Use the CM06 bit

in the CM0 register and bits CM16 to CM17 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 clock mode, the CM06 bit is set to 1 (divide-by-8 mode).

10.3.3

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

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

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

RA, RB, RC, and RD, the serial interface and the 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 stop.

10.3.4

fOCO

fOCO is an operating clock for the peripheral functions.

fOCO runs at the same frequency as the on-chip oscillator clock and can be used as the source for timer RA.

When the WAIT instruction is executed, the clocks fOCO does not stop.

10.3.5

fOCO40M

fOCO40M is used as the count source for timer RC and timer RD. fOCO40M is generated by the high-speed

on-chip oscillator and supplied by setting the FRA00 bit to 1.

When the WAIT instruction is executed, the clock fOCO40M does not stop.

fOCO40M can be used with supply voltage VCC = 3.0 to 5.5 V.

10.3.6

fOCO-F

fOCO-F is used as the count source for the A/D converter. fOCO-F is generated by the high-speed on-chip

oscillator and supplied by setting the FRA00 bit to 1.

When the WAIT instruction is executed, the clock fOCO-F does not stop.

10.3.7

fOCO-S

fOCO-S is an operating clock for the watchdog timer and voltage detection circuit. fOCO-S is supplied by

setting the CM14 bit to 0 (low-speed on-chip oscillator on) and uses the clock generated by the low-speed on-

chip oscillator. When the WAIT instruction is executed or in count source protect mode of the watchdog timer,

fOCO-S does not stop.

10.3.8

fOCO128

fOCO128 is generated by fOCO divided by 128.

The clock fOCO128 is used for capture signal of timer RC’s TRCGRA register and timer RD (channel 0).

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