R8C20 datasheet(91/501 Pages) RENESAS

91 / 501 page

R8C/20 Group, R8C/21 Group

10. Clock Generation Circuit

Rev.2.00 Aug 27, 2008

Page 75 of 458

REJ09B0250-0200

10.4.1.3

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 FRA01bit in the FRA0

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. Set the CM06 bit to 1 (divide-by-8

mode) when transiting to high-speed clock mode. When the FRA00 bit is set to 1, fOCO40M can be used for

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

watchdog timer and voltage detection circuit.

In this mode, stopping the XIN clock and 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.

When enabling reduced internal power consumption using the VCA20 bit, follow Figure 10.10 Procedure for

Enabling Reduced Internal Power Consumption Using VCA20 bit.

10.4.2

Wait Mode

Since the CPU clock stops in wait mode, the CPU operated in the CPU clock and the watchdog timer when

count source protection mode is disabled stops. The XIN clock and on-chip oscillator clock do not stop and the

peripheral functions using these clocks maintain 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. The power consumption can be reduced.

10.4.2.2

Entering Wait Mode

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

When the OCD2 bit in the OCD register is set to 1 (on-chip oscillator selected as system clock), set the

OCD1bit in the OCD register to 0 (oscillation stop detection interrupt disabled) before executing the WAIT

instruction.

If the MCU enters wait mode while the OCD1 bit is set to 1 (oscillation stop detection interrupt enabled),

current consumption is not reduced because the CPU clock does not stop.

10.4.2.3

Pin Status in Wait Mode

The I/O port is the status before wait mode was entered is maintained.

R8C20 Datasheet(PDF) 91 Page - Renesas Technology Corp