C8051F52X_12 Datasheet, PDF (142/221 Pages) Silicon Laboratories – 8/4/2 kB ISP Flash MCU Family

C8051F52x/F53x
SFR Definition 14.4. OSCXCN: External Oscillator Control
R
R/W
R/W
R/W
R/W
XTLVLD XOSCMD2 XOSCMD1 XOSCMD0 Reserved
Bit7
Bit6
Bit5
Bit4
Bit3
R/W
XFCN2
Bit2
R/W
XFCN1
Bit1
R/W
Reset Value
XFCN0 00000000
Bit0
SFR Address: 0xB1
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 = 0b; Must write 0b.
Bits2–0: 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  20 kHz
20 kHz f 58 kHz
58 kHz  f 155 kHz
155 kHz  f 415 kHz
415 kHz  f 1.1 MHz
1.1 MHz  f 3.1 MHz
3.1 MHz  f 8.2 MHz
8.2 MHz  f 25 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
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
Crystal Mode (Circuit from Figure 14.1, Option 1; XOSCMD = 11x)
Choose XFCN value to match crystal or resonator frequency.
RC Mode (Circuit from Figure 14.1, 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
C Mode (Circuit from Figure 14.1, Option 3; XOSCMD = 10x)
Choose K Factor (KF) for the oscillation frequency desired:
f = KF / (C x V_DD), where
f = frequency of clock in MHz
C = capacitor value the XTAL2 pin in pF
V_DD = Power Supply on MCU in volts
142
Rev. 1.4