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C8051F321-GMR Datasheet, PDF (121/250 Pages) Silicon Laboratories – Full Speed USB, 16 k ISP FLASH MCU Family | |||
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C8051F320/1
SFR Definition 13.3. 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
XFCN0
Bit0
Reset Value
00000000
SFR Address:
0xB1
Bit7:
Bits6â4:
Bit3:
Bits2â0:
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.
XOSCMD2â0: 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.
XFCN2â0: External Oscillator Frequency Control Bits.
000â111: See table below:
XFCN
000
001
010
011
100
101
110
111
Crystal (XOSCMD = 11x)
f ï£ 32 kHz
32 kHz ï¼ï f ï£ï 84 kHz
84 kHz ï¼ f ï£ï 225 kHz
225 kHz ï¼ f ï£ï 590 kHz
590 kHz ï¼ f ï£ï 1.5 MHz
1.5 MHz ï¼ f ï£ï 4 MHz
4 MHz ï¼ f ï£ï 10 MHz
10 MHz ï¼ f ï£ï 30 MHz
RC (XOSCMD = 10x)
f ï£ï 25 kHz
25 kHz ï¼ï f ï£ï 50 kHz
50 kHz ï¼ï f ï£ï 100 kHz
100 kHz ï¼ï f ï£ï 200 kHz
200 kHz ï¼ï f ï£ï 400 kHz
400 kHz ï¼ï f ï£ï 800 kHz
800 kHz ï¼ï f ï£ï 1.6 MHz
1.6 MHz ï¼ï f ï£ï 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 13.1, Option 1; XOSCMD = 11x)
Choose XFCN value to match crystal or resonator frequency.
RC MODE (Circuit from Figure 13.1, 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 kï
C MODE (Circuit from Figure 13.1, Option 3; XOSCMD = 10x)
Choose K Factor (KF) for the oscillation frequency desired:
f = KF / (C * VDD), where
f = frequency of clock in MHz
C = capacitor value the XTAL2 pin in pF
VDD = Power Supply on MCU in volts
Rev. 1.4
121
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