C8051F352 Datasheet, PDF (134/234 Pages) Silicon Laboratories – 8 k ISP Flash MCU Family

C8051F350/1/2/3
SFR Definition 17.3. 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
XFCN1
Bit1
R/W
Reset Value
XFCN0 00000000
Bit0
SFR Address: 0xB1
Bit7:
Bits6–4:
Bit3:
Bits2–0:
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.
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.
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 17.1, Option 1; XOSCMD = 11x)
Choose XFCN value to match crystal or resonator frequency.
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
RC MODE (Circuit from Figure 17.1, Option 2; XOSCMD = 10x)
Choose XFCN value to match frequency range:
f = 1.23(10³) / (R * C), where
f = frequency of clock in MHz
C = capacitor value in pF
R = Pull-up resistor value in kΩ
C MODE (Circuit from Figure 17.1, Option 3; XOSCMD = 10x)
Choose K Factor (KF) for the oscillation frequency desired:
f = KF / (C * 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
134
Rev. 1.1