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 110 of 730
Aug 05, 2011
10.2.3
System Clock Control Register 3 (CM3)
Notes:
1. When the MCU exits wait mode by a peripheral function interrupt, the CM30 bit is set to 0 (not in wait mode).
2. Set the CM35 bit to 0 in stop mode. When the MCU enters wait mode, if the CM35 bit is 1 (no division), the CM06
bit in the CM0 register is set to 0 (bits CM16 and CM17 in CM1 register enabled) and bits CM17 and CM16 are
set to 00b (divide-by-1 mode).
3. To enter wait mode or stop mode while the FMR27 bit in the FMR2 register is 1 (flash memory low-current-
consumption read mode enabled), set bits CM37 and CM36 to 00b (MCU exits using the CPU clock used
immediately before entering wait mode or stop mode) and set the CM35 bit to 0 (settings of CM06 bit in CM0
register and bits CM16b and CM17 in CM1 register enabled). During low-current-consumption read mode, do not
set the FMSTP bit in the FMR0 register to 1 (flash memory stops).
4. When bits CM37 and CM36 are set to 10b (high-speed on-chip oscillator clock selected), the following will be set
when the MCU exits wait mode or stop mode.
Bits CM42 to CM40 in CM4 register = 001b (fLOCO clock)
FRA00 bit in FRA0 register (high-speed on-chip oscillator on)
Bits CM42 to CM40 in CM4 register = 101b (fHOCO-F clock)
5. When bits CM37 and CM36 are set to 11b (XIN clock selected), the following will be set when the MCU exits wait
mode or stop mode.
OM05 bit in OM0 register = 1 (XIN clock oscillates)
OM13 bit in OM1 register = 1 (XIN-XOUT pin)
Bits CM42 to CM40 in CM4 register = 000b (XIN clock selected)
When entering wait mode while the CM05 bit in the CM0 register is 1 (XIN clock stops), if the XIN clock is
selected as the CPU clock used to exit wait mode, set the CM06 bit to 1 (divide-by-8 mode) and the CM35 bit to
0.
However, if an externally generated clock is used as the XIN clock, do not set bits CM37 and CM36 to 11b (XIN
clock selected).
Set the PRC0 bit in the PRCR register to 1 (write enabled) before rewriting the CM3 register.
Address 0000Bh
Bit
b7b6
b5b4b3
b2b1b0
Symbol
CM37
CM36
CM35
—
CM30
After Reset
0
000
0000
Bit
Symbol
Bit Name
Function
R/W
b0
CM30
Wait control bit (1)
0: Not in wait mode
1: MCU enters wait mode
R/W
b1
—
Nothing is assigned. The write value must be 0. The read value is 0.
—
b2
—
b3
—
b4
—
b5
CM35
CPU clock division ratio select bit when
exiting wait mode (2)
0: Settings of CM06 bit in CM0 register and bits
CM16 and CM17 in CM1 register enabled
1: No division
R/W
b6
CM36
System clock select bits when exiting
wait mode or stop mode (3)
b7 b6
0 0: MCU exits using the CPU clock used
immediately before entering wait mode or
stop mode
0 1: Do not set.
1 0: High-speed on-chip oscillator clock
selected (4)
1 1: XIN clock selected (5)
R/W
b7
CM37
R/W