Sfr Definition 14.4. Oscxcn: External Oscillator Control - Silicon Laboratories C8051F12 Series Manual

C8051F120/1/2/3/4/5/6/7 C8051F130/1/2/3

SFR Definition 14.4. OSCXCN: External Oscillator Control

R R/W
XTLVLD XOSCMD2 XOSCMD1 XOSCMD0
Bit7 Bit6
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:
XFCN Crystal (XOSCMD = 11x)
000
32 kHz < f ≤ 84 kHz
001
84 kHz < f ≤ 225 kHz
010
225 kHz < f ≤ 590 kHz
011
590 kHz < f ≤ 1.5 MHz
100
1.5 MHz < f ≤ 4 MHz
101
4 MHz < f ≤ 10 MHz
110
10 MHz < f ≤ 30 MHz
111
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:
3
f = 1.23(10 ) / (R * C) , where
f = frequency of oscillation in MHz
C = capacitor value in pF
R = Pullup resistor value in k Ω
C MODE (Circuit from Figure 14.1, Option 3; XOSCMD = 10x)
Choose K Factor (KF) for the oscillation frequency desired:
f = KF / (C * V
DD
f = frequency of oscillation in MHz
C = capacitor value on XTAL1, XTAL2 pins in pF
V = Power Supply on MCU in Volts
DD
R/W R/W R
-
Bit5 Bit4 Bit3
RC (XOSCMD = 10x)
f ≤ 32 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
) , where
Rev. 1.4
R/W R/W
XFCN2 XFCN1
Bit2 Bit1
SFR Address:
C (XOSCMD = 10x)
f ≤ 25 kHz
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
R/W Reset Value
XFCN0 00000000
Bit0
0x8C
SFR Page: F
189