
R8C/3GM Group
9. Clock Generation Circuit
R01UH0284EJ0100 Rev.1.00
Aug 09, 2011
9.2.6
High-Speed On-Chip Oscillator Control Register 0 (FRA0)
Notes:
1. Change the FRA01 bit in the following conditions.
FRA00 = 1 (high-speed on-chip oscillator on)
The CM14 bit in the CM1 register = 0 (low-speed on-chip oscillator on)
Bits FRA22 to FRA20 in the FRA2 register:
All division mode can be set when VCC = 2.7 V to 5.5 V
000b to 111b
Divide ratio of 8 or more when VCC = 1.8 V to 5.5 V
110b to 111b (divide-by-8 or more)
2. When setting the FRA01 bit to 0 (low-speed on-chip oscillator selected), do not set the FRA00 bit to 0 (high-
speed on-chip oscillator off) at the same time. Set the FRA00 bit to 0 after setting the FRA01 bit to 0.
3. When setting the FRA01 bit to 1 (high-speed on-chip oscillator selected) and stopping the low-speed on-chip
oscillator, wait for one or more cycles of the low-speed on-chip oscillator and then set the CM14 bit in the CM1
register to 1 (low-speed on-chip oscillator off).
Set the PRC0 bit in the PRCR register to 1 (write enabled) before rewriting the FRA0 register.
9.2.7
High-Speed On-Chip Oscillator Control Register 1 (FRA1)
Set the PRC0 bit in the PRCR register to 1 (write enabled) before rewriting the FRA1 register.
Also, rewrite the FRA1 register when the FRA00 bit in the FRA0 register is set 0 (high-speed on-chip oscillator
off).
Address 0023h
Bit
b7b6b5
b4b3b2
b1b0
Symbol
After Reset
000
00
Bit
Symbol
Bit Name
Function
R/W
b0
FRA00
High-speed on-chip oscillator enable bit
0: High-speed on-chip oscillator off
1: High-speed on-chip oscillator on
R/W
b1
FRA01
High-speed on-chip oscillator select bit
(1) 0: Low-speed on-chip oscillator selected
(2)1: High-speed on-chip oscillator selected
(3)R/W
b2
—
Reserved bit
Set to 0.
R/W
b3
FRA03
fOCO128 clock select bit
0: fOCO-S divided by 128 selected
1: fOCO-F divided by 128 selected
R/W
b4
—
Nothing is assigned. If necessary, set to 0. When read, the content is 0.
—
b5
—
b6
—
b7
—
Address 0024h
Bit
b7b6b5
b4b3b2
b1b0
Symbol
——
———
After Reset
When shipping
Bit
Function
R/W
b7-b0 The frequency of the high-speed on-chip oscillator can be adjusted by setting as follows:
40 MHz:
FRA1 = value after reset, FRA3 = value after reset
36.864 MHz: Transfer the value in the FRA4 register to the FRA1 register and the value in
the FRA5 register to the FRA3 register.
32 MHz:
Transfer the value in the FRA6 register to the FRA1 register and the value in
the FRA7 register to the FRA3 register.
R/W