C8051F120 Datasheet, PDF (191/356 Pages) Silicon Laboratories – Mixed Signal ISP Flash MCU Family

C8051F120/1/2/3/4/5/6/7
C8051F130/1/2/3
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
Reset Value
XFCN0 00000000
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 = 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 * VDD), where
f = frequency of oscillation in MHz
C = capacitor value on XTAL1, XTAL2 pins in pF
VDD = 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
Figure 14.5. OSCXCN: External Oscillator Control Register
Rev. 1.3
193