C8051F007 View Datasheet(PDF) - Silicon Laboratories

Part Name

Description

MFG CO.

C8051F007

Mixed-Signal 32KB ISP FLASH MCU Family

Silicon Laboratories 

C8051F000/1/2/5/6/7

C8051F010/1/2/5/6/7

Figure 14.3. OSCXCN: External Oscillator Control Register

R

R/W

R/W

R/W

R/W

XTLVLD XOSCMD2 XOSCMD1 XOSCMD0

-

Bit7

Bit6

Bit5

Bit4

Bit3

R/W

XFCN2

Bit2

R/W

XFCN1

Bit1

R/W

XFCN0

Bit0

Bit7: XTLVLD: Crystal Oscillator Valid Flag

(Valid only when XOSCMD = 1xx.)

0: Crystal Oscillator is unused or not yet stable

1: Crystal Oscillator is running and stable (should read 1ms after Crystal Oscillator is

enabled to avoid transient condition).

Bits6-4: XOSCMD2-0: External Oscillator Mode Bits

00x: Off. XTAL1 pin is grounded internally.

010: System Clock from External CMOS Clock on XTAL1 pin.

011: System Clock from External CMOS Clock on XTAL1 pin divided by 2.

10x: RC/C Oscillator Mode with divide by 2 stage.

110: Crystal Oscillator Mode

111: Crystal Oscillator Mode with divide by 2 stage.

Bit3: RESERVED. Read = undefined, Write = don’t care

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

000-111: see table below

Reset Value

00110000

SFR Address:

0xB1

XFCN

000

001

010

011

100

101

110

111

Crystal (XOSCMD =

11x)

f ≤ 12.5kHz

12.5kHz < f ≤ 30.3kHz

30.35kHz < f ≤ 93.8kHz

93.8kHz < f ≤ 267kHz

267kHz < f ≤ 722kHz

722kHz < f ≤ 2.23MHz

2.23MHz < f ≤ 6.74MHz

f > 6.74MHz

RC (XOSCMD = 10x)

f ≤ 25kHz

25kHz < f ≤ 50kHz

50kHz < f ≤ 100kHz

100kHz < f ≤ 200kHz

200kHz < f ≤ 400kHz

400kHz < f ≤ 800kHz

800kHz < f ≤ 1.6MHz

1.6MHz < f ≤ 3.2MHz

C (XOSCMD = 10x)

K Factor = 0.44

K Factor = 1.4

K Factor = 4.4

K Factor = 13

K Factor = 38

K Factor = 100

K Factor = 420

K Factor = 1400

CRYSTAL MODE (Circuit from Figure 14.1, Option 1; XOSCMD = 11x)

Choose XFCN value to match the crystal or ceramic resonator frequency.

RC MODE (Circuit from Figure 14.1, Option 2; XOSCMD = 10x)

Choose oscillation frequency range where:

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

f = frequency of oscillation in MHz

C = capacitor value in pF

R = Pull-up resistor value in kΩ

C MODE (Circuit from Figure 14.1, Option 3; XOSCMD = 10x)

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

f = KF / (C * AV+), where

f = frequency of oscillation in MHz

C = capacitor value on XTAL1, XTAL2 pins in pF

AV+ = Analog Power Supply on MCU in volts

101

Rev. 1.7

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