Silicon Laboratories C8051F342 Two-Way Radio User Manual


 
Rev. 0.5 141
C8051F340/1/2/3/4/5/6/7
SFR Definition 14.4. OSCXCN: External Oscillator Control
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 = 0, Write = don't care.
Bits2–0: XFCN2–0: External Oscillator Frequency Control Bits.
000-111: See table below:
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(10
3
) / (R x C), where
f = frequency of clock in MHz
C = capacitor value in pF
R = Pull-up 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
R R/W R/W R/W R R/W R/W R/W Reset Value
XTLVLD XOSCMD2 XOSCMD1 XOSCMD0 - XFCN2 XFCN1 XFCN0 00000000
Bit7 Bit6 Bit5 Bit4 Bit3 Bit2 Bit1 Bit0 SFR Address:
0xB1
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 84kHz 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