R8C2K Datasheet, PDF (417/471 Pages) Renesas Technology Corp – MCU

R8C/2K Group, R8C/2L Group
21. Reducing Power Consumption
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.
Transfer FMSTP bit setting program to RAM
Jump to FMSTP bit setting program
(The subsequent processing is executed by
the program in the RAM)
FMSTP bit setting program
After writing 0 to FMR01 bit, write 1 (CPU
rewrite mode enabled)
Write 1 to FMSTP bit (flash memory stops. low
power consumption state)⁽¹⁾
Enter low-speed on-chip oscillator mode
Stop high-speed on-chip oscillator
Process in low-speed on-chip oscillator mode
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.
FMR01, FMSTP: Bits in FMR0 register
Switch clock source for CPU clock⁽²⁾
Write 0 to FMSTP bit (flash memory operates)
Write 0 to FMR01 bit (CPU rewrite mode
disabled)
Wait until flash memory circuit stabilizes
(30 µs)⁽³⁾
Jump to specified address in flash memory
Figure 21.2 Handling Procedure Example of Low Power Consumption Using FMSTP Bit
Rev.1.10 Dec 21, 2007 Page 400 of 450
REJ09B0406-0110