R8C/38T-A Group
10. Power Control
Under development Preliminary document
Specifications in this document are tentative and subject to change.
R01UH0241EJ0010 Rev.0.10
Page 128 of 730
Aug 05, 2011
10.6.11 Low-Current-Consumption Read Mode
In low-speed clock and low-speed on-chip oscillator mode, the current consumption when reading the flash
memory can be reduced by setting the FMR27 bit in the FMR2 register to 1 (low-current-consumption read
mode enabled).
Low-current-consumption read mode can be used when the CPU clock is set to either of the following:
The CPU clock is set to the low-speed on-chip oscillator clock divided by 4, 8, or 16.
The CPU clock is set to the XCIN clock divided by 1 (no division), 2, 4, or 8.
However, do not use low-current-consumption read mode when the frequency of the selected CPU clock is 3
kHz or below.
After setting the division ratio of the CPU clock, set the FMR27 bit to 1.
When entering wait mode or stop mode, set the FMR27 bit to 0 (low-current-consumption read mode disabled)
before entering. Do not enter wait mode or stop mode while the FMR27 bit is 1.
Figure 10.7
Procedure for Using Flash Memory Low-Current-Consumption Read Mode
FMR27: Bit in FMR2 register
Notes:
1. To set the FMR27 bit to 1 (low-current-consumption read mode enabled), first write 0 and then write 1
immediately.
Interrupts and DTC activation must be disabled between writing 0 and writing 1.
2. In low-current-consumption read mode, set the FMR01 bit in the FMR0 register to 0 (CPU rewrite mode
disabled).
When entering wait mode or stop mode, set the FMR27 bit to 0 (low-current-consumption read mode disabled)
before entering. Do not enter wait mode or stop mode while the FMR27 bit is 1.
Handling procedure for enabling
low-current-consumption read mode
using FMR27
Enter low-speed clock mode or
low-speed on-chip oscillator mode
Stop the high-speed on-chip oscillator clock
FMR27
1
(low-current-consumption read mode enabled)
(1)
Enter low-current-consumption read mode
(2)
FMR27
0
(low-current-consumption read mode disabled)
Start the high-speed on-chip oscillator clock
(Wait until the high-speed on-chip oscillator
clock oscillation stabilizes)
Enter high-speed on-chip oscillator mode
Step (1)
Step (2)
Step (3)
Step (4)
Step (5)
Step (6)
Step (7)
Step (8)