Renesas R8C/20 User Manual

R8C/20 Group, R8C/21 Group 10. Clock Generation Circuit
Rev.2.00 Aug 27, 2008 Page 69 of 458
REJ09B0250-0200
Figure 10.5 Registers FRA0 and FRA1
High-Speed On-Chip Oscillator Control Register 0
(1)
Symbol Address After Reset
FRA0
0023h 00h
Bit Symbol Bit Name Function RW
NOTES:
1.
2.
3.
b7 b6 b5 b4 b3 b2 b1 b0
000000
FRA00 RW
FRA01 RW
High-speed on-chip oscillator enable
bit
0 : High-speed on-chip oscillator off
1 : High-speed on-chip oscillator on
High-speed on-chip oscillator select
bit
(2)
0 : Selects low -speed on-chip oscillator
(3)
1 : Selects high-speed on-chip oscillator
Change the FRA01 bit under the follow ing conditions.
• FRA00 = 1 (high-speed on-chip oscillation)
• The CM14 bit in the CM1 register = 0 (low -speed on-chip oscillator on)
• Bits FRA22 to FRA20 in the FRA2 register
All divide ratio mode settings are supported w hen VCC = 3.0 V to 5.5 V (J version) 000b to 111b
Divide ratio of 4 or more w hen VCC = 2.7 V to 5.5 V and K version 010b to 111b
When setting the FRA01 bit to 0 (selects low -speed on-chip oscillator), do not set the FRA00 bit to 0 (40MHz on-chip
oscillator off) at the same time.
Set the FRA00 bit to 0 after setting the FRA01 bit to 0.
—
(b7-b2)
Reserved bits Set to 0
RW
Set the PRC0 bit in the PRCR register to 1 (enables w riting) before rew riting to the FRA0 register.
High-Speed On-Chip Oscillator Control Register 1
(1)
Symbol Address After Reset
FRA1
0024h
When Shipping
RW
NOTES:
1.
2.
b7 b0
When changing the values of the FRA1 register, adjust the FRA1 register so that the frequency of the high-speed
on-chip oscillator clock w ill be 40 MHz or less.
Set the PRC0 bit in the PRCR register to 1 (w rite enable) before rew riting to the FRA1 register.
When adjusting the FRA1 register, set the value of the FRA1 register to 40 MHz and below .
RW
Function
The frequency of high-speed on-chip oscillator is adjusted w ith bits 0 to 7.
High-speed on-chip oscillator frequency = 40 MHz (FRA1 register = value w hen shipping)
Set the value of the FRA1 register to smaller, the frequency w ill be higher
Set the value of the FRA1 register to larger, the frequency w ill be low er
(2)

Renesas R8C/20 Specifications

General

Brand	Renesas
Model	R8C/20
Category	Control Unit
Language	English