R8CSLASH20 datasheet(85/501 Pages) RENESAS

85 / 501 page

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

NOTES:

b7 b6 b5 b4 b3 b2 b1 b0

000000

FRA00

FRA01

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

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

NOTES:

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 .

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)

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