C8051F317 查看數據表（PDF） - Silicon Laboratories

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C8051F317

8/16 kB ISP Flash MCU Family

Silicon Laboratories 

C8051F310/1/2/3/4/5/6/7

SFR Definition 12.4. OSCXCN: External Oscillator Control

R

R/W

R/W

R/W

R

XTLVLD XOSCMD2 XOSCMD1 XOSCMD0

Bit7

Bit6

Bit5

Bit4

Bit3

R/W

XFCN2

Bit2

R/W

XFCN1

Bit1

R/W

XFCN0

Bit0

Reset Value

00000000

SFR Address:

0xB1

Bit7:

Bits6–4:

Bit3:

Bits2–0:

XTLVLD: Crystal Oscillator Valid Flag.

(Read only when XOSCMD = 11x.)

0: Crystal Oscillator is unused or not yet stable.

1: Crystal Oscillator is running and stable.

XOSCMD2-0: External Oscillator Mode Bits.

00x: External Oscillator circuit off.

010: External CMOS Clock Mode.

011: External CMOS Clock Mode with divide by 2 stage.

100: RC Oscillator Mode.

101: Capacitor Oscillator Mode.

110: Crystal Oscillator Mode.

111: Crystal Oscillator Mode with divide by 2 stage.

RESERVED. Read = 0, Write = don't care.

XFCN2-0: External Oscillator Frequency Control Bits.

000-111: See table below:

XFCN

000

001

010

011

100

101

110

111

Crystal (XOSCMD = 11x)

f ≤ 32 kHz

32 kHz < f ≤ 84 kHz

84 kHz < f ≤ 225 kHz

225 kHz < f ≤ 590 kHz

590 kHz < f ≤ 1.5 MHz

1.5 MHz < f ≤ 4 MHz

4 MHz < f ≤ 10 MHz

10 MHz < f ≤ 30 MHz

RC (XOSCMD = 10x)

f ≤ 25 kHz

25 kHz < f ≤ 50 kHz

50 kHz < f ≤ 100 kHz

100 kHz < f ≤ 200 kHz

200 kHz < f ≤ 400 kHz

400 kHz < f ≤ 800 kHz

800 kHz < f ≤ 1.6 MHz

1.6 MHz < f ≤ 3.2 MHz

CRYSTAL MODE (Circuit from Figure 12.1, Option 1; XOSCMD = 11x)

Choose XFCN value to match crystal frequency.

C (XOSCMD = 10x)

K Factor = 0.87

K Factor = 2.6

K Factor = 7.7

K Factor = 22

K Factor = 65

K Factor = 180

K Factor = 664

K Factor = 1590

RC MODE (Circuit from Figure 12.1, Option 2; XOSCMD = 10x)

Choose XFCN value to match frequency range:

f = 1.23(103) / (R x C), where

f = frequency of clock in MHz

C = capacitor value in pF

R = Pullup resistor value in kΩ

C MODE (Circuit from Figure 12.1, Option 3; XOSCMD = 10x)

Choose K Factor (KF) for the oscillation frequency desired:

f = KF / (C x VDD), where

f = frequency of clock in MHz

C = capacitor value the XTAL2 pin in pF

VDD = Power Supply on MCU in volts

Rev. 1.6

121

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