
C8051F120/1/2/3/4/5/6/7
C8051F130/1/2/3
Rev. 1.4
189
SFR Definition 14.4. OSCXCN: External Oscillator Control
Bit7:
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.
Bits6–4: 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.
Bit3:
RESERVED. Read = 0, Write = don't care.
Bits2–0: XFCN2–0: External Oscillator Frequency Control Bits.
000-111: see table below:
CRYSTAL MODE
Choose XFCN value to match crystal frequency.
RC MODE
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
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
R
R/W
R
R/W
Reset Value
XTLVLD XOSCMD2 XOSCMD1 XOSCMD0
-
XFCN2
XFCN1
XFCN0
00000000
Bit7
Bit6
Bit5
Bit4
Bit3
Bit2
Bit1
Bit0
SFR Address:
SFR Page:
0x8C
F
XFCN
Crystal (XOSCMD = 11x)
RC (XOSCMD = 10x)
C (XOSCMD = 10x)
000
f
32 kHz
f
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