R8C18 datasheet(79/257 Pages) RENESAS

79 / 257 page

R8C/18 Group, R8C/19 Group

10. Clock Generation Circuit

Rev.1.30

Apr 14, 2006

Page 64 of 233

REJ09B0222-0130

10.4.1.1

High-Speed Mode

The main clock divided by 1 (no division) provides the CPU clock. If the CM14 bit is set to 0 (low-

speed on-chip oscillator on) or the HRA00 bit in the HRA0 register is set to 1 (high-speed on-chip

oscillator on), fRING and fRING128 can be used as timers X and C. When the HRA00 bit is set to 1,

fRING-fast can be used as timer C. When the CM14 bit is set to 0 (low-speed on-chip oscillator on),

fRING-S can be used for the watchdog timer and voltage detection circuit.

10.4.1.2

Medium-Speed Mode

The main clock divided by 2, 4, 8, or 16 provides the CPU clock. If the CM14 bit is set to 0 (low-speed

on-chip oscillator on) or the HRA00 bit in the HRA0 register is set to 1 (high-speed on-chip oscillator

on), fRING and fRING128 can be used as timers X and C. When the HRA00 bit is set to 1, fRING-

fast can be used as timer C. When the CM14 bit is set to 0 (low-speed on-chip oscillator on), fRING-

S can be used for the watchdog timer and voltage detection circuit.

10.4.1.3

High-Speed and Low-Speed On-Chip Oscillator Modes

The on-chip oscillator clock divided by 1 (no division), 2, 4, 8, or 16 provides the CPU clock. The on-

chip oscillator clock is also the clock source for the peripheral function clocks. When the HRA00 bit is

set to 1, fRING-fast can be used as timer C. When the CM14 bit is set to 0 (low-speed on-chip

oscillator on), fRING-S can be used for the watchdog timer and voltage detection circuit.

10.4.2

Wait Mode

Since the CPU clock stops in wait mode, the CPU, which operates using the CPU clock and the

watchdog timer when count source protection mode is disabled stop. The main clock and on-chip

oscillator clock do not stop and the peripheral functions using these clocks continue operating.

10.4.2.1

Peripheral Function Clock Stop Function

If the CM02 bit is set to 1 (peripheral function clock stops in wait mode), the f1, f2, f4, f8, and f32

clocks stop in wait mode. This reduces power consumption.

10.4.2.2

Entering Wait Mode

The MCU enters wait mode when the WAIT instruction is executed.

10.4.2.3

Pin Status in Wait Mode

The status before wait mode was entered is maintained.

R8C18 Datasheet(PDF) 79 Page - Renesas Technology Corp