C8051F300/1/2/3/4/5
100
Rev. 2.9
SFR Definition 11.3. 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 with divide by 2 stage.
101: Capacitor 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:
CRYSTAL MODE
(Circuit from Figure 11.1, Option 1; XOSCMD = 11x)
Choose XFCN value to match crystal frequency.
RC MODE
(Circuit from Figure 11.1, Option 2; XOSCMD = 10x)
Choose XFCN value to match frequency range:
f = 1.23(10
3
) / (R x C)
, where
f = frequency of oscillation in MHz
C = capacitor value in pF
R = Pull-up resistor value in k
Ω
C MODE
(Circuit from Figure 11.1, Option 3; XOSCMD = 10x)
Choose K Factor (KF) for the oscillation frequency desired:
f = KF / (C x V
DD
)
, where
f = frequency of oscillation 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
≤
84 kHz
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
Summary of Contents for C8051F300
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