R8CSLASH2G datasheet(120/344 Pages) RENESAS

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R8C/2G Group

11. Clock Generation Circuit

Rev.1.00

Apr 04, 2008

Page 100 of 318

REJ09B0387-0100

11.4.1.1

High-Speed On-Chip Oscillator Mode

The high-speed on-chip oscillator is used as the on-chip oscillator clock when the HRA00 bit in the HRA0

chip oscillator divided by 1 (no division), 2, 4, 8, or 16 provides the CPU clock. Set the CM06 bit to 1 (divide-

by-8 mode) when transiting to high-speed clock mode.

When the CM14 bit is set to 0 (low-speed on-chip oscillator on), fOCO-S can be used as the watchdog timer

and voltage detection circuit.

11.4.1.2

Low-Speed On-Chip Oscillator Mode

If the CM14 bit in the CM1 register is set to 0 (low-speed on-chip oscillator on) or the HRA01 bit in the HRA0

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 CM14 bit is set to 0 (low-speed on-chip oscillator on), fOCO-S can be used as the watchdog timer

and voltage detection circuit.

In this mode, stopping the high-speed on-chip oscillator, and setting the FMR47 bit in the FMR4 register to 1

(flash memory low consumption current read mode enabled) enables low consumption operation.

To enter wait mode from low-speed on-chip oscillator mode, setting the VCA20 bit in the VCA2 register to 1

(internal power low consumption enabled) enables lower consumption current in wait mode.

Refer to 21. Reducing Power Consumption for how to reduce the power consumption.

11.4.1.3

Low-Speed Clock Mode

The XCIN clock divided by 1 (no division), 2, 4, 8, or 16 provides the CPU clock. Set the CM06 bit to 1 (divide

by-8 mode) when transiting to high-speed on-chip oscillator mode, low-speed on-chip oscillator mode. 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), fOCO can be used as timer RA.

When the CM14 bit is set to 0 (low-speed on-chip oscillator on), fOCO-S can be used as the watchdog timer

and voltage detection circuit.

In this mode, stopping the high-speed on-chip oscillator, and setting the FMR47 bit in the FMR4 register to 1

(flash memory low consumption current read mode enabled) enables low consumption operation.

To enter wait mode from low-speed clock mode, setting the VCA20 bit in the VCA2 register to 1 (internal

power low consumption enabled) enables lower consumption current in wait mode.

Refer to 21. Reducing Power Consumption for how to reduce the power consumption.

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