C8051F2XX Datasheet, PDF (99/146 Pages) Silicon Laboratories – Mixed Signal 8 kB ISP Flash MCU Family

C8051F2xx
SFR Definition 13.2. OSCXCN: External Oscillator Control
R
R/W
R/W
R/W
R/W
XTLVLD XOSCMD2 XOSCMD1 XOSCMD0 -
Bit7
Bit6
Bit5
Bit4
Bit3
R/W
XFCN2
Bit2
R/W
XFCN1
Bit1
R/W
XFCN0
Bit0
Reset Value
00110000
SFR Address:
0xB1
Bit7:
Bits6–4:
Bit3:
Bits2–0:
XTLVLD: Crystal Oscillator Valid Flag
(Valid only when XOSCMD = 1xx.)
0: Crystal Oscillator is unused or not yet stable
1: Crystal Oscillator is running and stable
XOSCMD2–0: External Oscillator Mode Bits
00x: Off. XTAL1 pin is grounded internally.
010: System Clock from External CMOS Clock on XTAL1 pin.
011: System Clock from External CMOS Clock on XTAL1 pin divided by 2.
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 = undefined, 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 ≤ 12.5 kHz
12.5 kHz < f ≤ 30.3 kHz
30.35 kHz < f ≤ 93.8 kHz
93.8 kHz < f ≤ 26 7kHz
267 kHz < f ≤ 722 kHz
722 kHz < f ≤ 2.23 MHz
2.23 MHz < f ≤ 6.74 MHz
f > 6.74 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 = 0.44
K Factor = 1.4
K Factor = 4.4
K Factor = 13
K Factor = 38
K Factor = 100
K Factor = 420
K Factor = 1400
CRYSTAL MODE (Circuit from Figure 13.1, Option 1; XOSCMD = 11x)
Choose XFCN value to match the crystal frequency.
RC MODE (Circuit from Figure 13.1, Option 2; XOSCMD = 10x)
Choose oscillation frequency range where:
f = 1.23(10³) / (R x 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 13.1, Option 3; XOSCMD = 10x)
Choose K Factor (KF) for the oscillation frequency desired:
f = KF / (C x AV+), where
f = frequency of oscillation in MHz
C = capacitor value on XTAL1, XTAL2 pins in pF
V_DD = Power supply voltage on MCU in volts
Rev. 1.6
99