C8051F124-GQR Datasheet, PDF (189/350 Pages) Silicon Laboratories – Mixed Signal ISP Flash MCU Family

C8051F120/1/2/3/4/5/6/7
C8051F130/1/2/3
SFR Definition 14.4. 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
R/W
Reset Value
XFCN1 XFCN0 00000000
Bit1
Bit0
SFR Address: 0x8C
SFR Page: F
Bit7:
Bits6–4:
Bit3:
Bits2–0:
XTLVLD: Crystal Oscillator Valid Flag.
(Valid 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 (External CMOS Clock input on XTAL1 pin).
011: External CMOS Clock Mode with divide by 2 stage (External CMOS Clock input on
XTAL1 pin).
10x: RC/C Oscillator Mode with divide by 2 stage.
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 14.1, Option 1; XOSCMD = 11x)
Choose XFCN value to match crystal frequency.
RC MODE (Circuit from Figure 14.1, Option 2; XOSCMD = 10x)
Choose XFCN value to match frequency range:
f = 1.23(10³) / (R * C), where
f = frequency of oscillation in MHz
C = capacitor value in pF
R = Pullup resistor value in k
C MODE (Circuit from Figure 14.1, Option 3; XOSCMD = 10x)
Choose K Factor (KF) for the oscillation frequency desired:
f = KF / (C * V_DD), where
f = frequency of oscillation in MHz
C = capacitor value on XTAL1, XTAL2 pins in pF
V_DD = Power Supply on MCU in Volts
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
Rev. 1.4
189