R8C2K datasheet(417/471 Pages) RENESAS

417 / 471 page

R8C/2K Group, R8C/2L Group

21. Reducing Power Consumption

Rev.1.10

Dec 21, 2007

Page 400 of 450

REJ09B0406-0110

21.2.9

Stopping Flash Memory

In low-speed on-chip oscillator mode, power consumption can be further reduced by stopping the flash memory

using the FMSTP bit in the FMR0 register.

Access to the flash memory is disabled by setting the FMSTP bit to 1 (flash memory stops). The FMSTP bit

must be written to by a program transferred to RAM.

When the MUC enters stop mode or wait mode while CPU rewrite mode is disabled, the power for the flash

memory is automatically turned off. It is turned back on again after the MCU exit stop mode or wait mode. This

eliminates the need to set the FMR0 register.

Figure 21.2 shows the Handling Procedure Example of Low Power Consumption Using FMSTP Bit.

Figure 21.2

Handling Procedure Example of Low Power Consumption Using FMSTP Bit

FMSTP bit setting program

Transfer FMSTP bit setting program to RAM

Jump to FMSTP bit setting program

(The subsequent processing is executed by

the program in the RAM)

After writing 0 to FMR01 bit, write 1 (CPU

rewrite mode enabled)

Enter low-speed on-chip oscillator mode

Process in low-speed on-chip oscillator mode

Write 0 to FMR01 bit (CPU rewrite mode

disabled)

Jump to specified address in flash memory

NOTES:

1. After setting the FMR01 bit to 1 (CPU rewrite mode enabled),

set the FMSTP bit to 1 (flash memory stops).

2. Before switching the CPU clock source, make sure the designated

clock is stable.

3. Insert a 30

µs wait time by a program.

Do not access to the flash memory during this wait time.

Write 1 to FMSTP bit (flash memory stops. low

power consumption state)(1)

Wait until flash memory circuit stabilizes

(30

µs)(3)

Write 0 to FMSTP bit (flash memory operates)

Switch clock source for CPU clock(2)

FMR01, FMSTP: Bits in FMR0 register

Stop high-speed on-chip oscillator

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