C8051F310 datasheet(121/224 Pages) ETC1

121 / 224 page

Rev. 1.6

121

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

SFR Definition 12.4. OSCXCN: External Oscillator Control

Bit7:

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.

Bits6–4: 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.

Bit3:

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

Bits2–0: XFCN2-0: External Oscillator Frequency Control Bits.

000-111: See table below:

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

Choose XFCN value to match crystal frequency.

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 k

Ω

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

R/W

Reset Value

XTLVLD XOSCMD2 XOSCMD1 XOSCMD0

XFCN2

XFCN1

XFCN0

00000000

Bit7

Bit6

Bit5

Bit4

Bit3

Bit2

Bit1

Bit0

SFR Address:

0xB1

XFCN

Crystal (XOSCMD = 11x)

RC (XOSCMD = 10x)

C (XOSCMD = 10x)

000

≤ 32 kHz

≤ 25 kHz

K Factor = 0.87

001

32 kHz

< f ≤ 84 kHz

25 kHz

< f ≤ 50 kHz

K Factor = 2.6

010

84 kHz

< f ≤ 225 kHz

50 kHz

< f ≤ 100 kHz

K Factor = 7.7

011

225 kHz

< f ≤ 590 kHz

100 kHz

< f ≤ 200 kHz

K Factor = 22

100

590 kHz

< f ≤ 1.5 MHz

200 kHz

< f ≤ 400 kHz

K Factor = 65

101

1.5 MHz

< f ≤ 4 MHz

400 kHz

< f ≤ 800 kHz

K Factor = 180

110

4 MHz

< f ≤ 10 MHz

800 kHz

< f ≤ 1.6 MHz

K Factor = 664

111

10 MHz

< f ≤ 30 MHz

1.6 MHz

< f ≤ 3.2 MHz

K Factor = 1590

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