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R8C/2G Group

21. Reducing Power Consumption

Rev.1.00

Apr 04, 2008

Page 272 of 318

REJ09B0387-0100

21.2.8

Reducing Internal Power Consumption

When the MCU enters wait mode using low-speed clock mode or low-speed on-chip oscillator mode, internal

power consumption can be reduced by using the VCA20 bit in the VCA2 register. Figure 21.1 shows the

Handling Procedure of Internal Power Low Consumption Using VCA20 Bit. To enable internal power low

consumption by the VCA20 bit, follow Figure 21.1 Handling Procedure of Internal Power Low Consumption

Using VCA20 Bit.

Figure 21.1

Handling Procedure of Internal Power Low Consumption Using VCA20 Bit

NOTES:

1. Execute this routine to handle all interrupts generated in wait mode.

However, this does not apply if it is not necessary to start high-speed on-chip oscillator during the interrupt routine.

2. Do not set the VCA20 bit to 0 with the instruction immediately after setting the VCA20 bit to 1. Also, do not do the opposite.

3. When entering wait mode, follow 11.5.2 Wait Mode.

Handling procedure of internal power

low consumption enabled by VCA20 bit

Enter low-speed clock mode or low-speed

on-chip oscillator mode

Stop high-speed on-chip oscillator clock

VCA20

← 1 (internal power low consumption

enabled)(2)

Enter wait mode(3)

VCA20

← 0 (internal power low consumption

disabled)(2)

Start high-speed on-chip oscillator clock

(Wait until high-speed on-chip oscillator clock

oscillation stabilizes)

In interrupt routine

VCA20

← 0 (internal power low consumption

disabled)(2)

Start high-speed on-chip oscillator clock

Enter high-speed on-chip oscillator mode

Enter low-speed clock mode or

low-speed on-chip oscillator mode

Exit wait mode by interrupt

Stop high-speed on-chip oscillator clock

VCA20

← 1 (internal power low consumption

enabled)(2, 3)

Interrupt handling completed

Step (1)

Step (2)

Step (3)

Step (4)

Step (5)

Step (6)

Step (7)

Step (5)

Step (6)

Step (7)

(Wait until high-speed on-chip oscillator clock

oscillation stabilizes)

Step (1)

Step (2)

Step (3)

If it is necessary to start

the high-speed on-chip

oscillator in the interrupt

routine, execute steps (5)

to (8) in the interrupt

routine.

If high-speed on-chip

oscillator is started in the

interrupt routine, execute

steps (1) to (3) at the last of

the interrupt routine.

(Note 1)

Interrupt handling

VCA20: Bit in VCA2 register

Step (8)

Enter high-speed on-chip oscillator mode

Step (8)

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