Silicon Laboratories C8051F347 - Manual (Page 131)

Rev. 1.3 131
C8051F340/1/2/3/4/5/6/7/8/9/A/B/C/D
14. Oscillators
C8051F34x devices include a programmable internal high-frequency oscillator, a programmable internal
low-frequency oscillator (C8051F340/1/2/3/4/5/8/9/A/B/C/D), an external oscillator drive circuit, and a 4x
Clock Multiplier. The internal high-frequency and low-frequency oscillators can be enabled/disabled and
adjusted using the special function registers, as shown in Figure 14.1. The system clock (SYSCLK) can be
derived from either of the internal oscillators, the external oscillator circuit, or the 4x Clock Multiplier divided
by 2. The USB clock (USBCLK) can be derived from the internal oscillator, external oscillator, or 4x Clock
Multiplier. Oscillator electrical specifications are given in Table 14.1.
Figure 14.1. Oscillator Diagram
Clock Multiplier
OSC
Input
Circuit
XT
L
V
LD
XTAL1
XTAL2
Option 2
VDD
XTAL2
Option 1
10M 
Option 3
XTAL2
Option 4
XTAL2
OSCXCN
XT
LVL
D
XO
SC
M
D
2
XO
SC
M
D
1
XO
SC
M
D
0
XF
CN2
XF
CN1
XF
CN0
CLKMUL
MULEN MUL
INIT
M
UL
RDY
MUL
SEL1
MUL
SEL0
Programmable High-
Frequency Oscillator
EN
OSCICL OSCICN
IOSCEN
IF
RD
Y
SUS
PEND
IF
CN1
IF
CN0
EXOSC / 2
x 2 x 2 EXOSC
IOSC
SYSCLK
EXOSC
EXOSC / 2
EXOSC / 3
EXOSC / 4
IOSC / 2
USBCLK
U
SBCL
K
2-
0
CLKSEL
U
SBCL
K2
U
SBCL
K1
U
SBCL
K0
CL
K
S
L
2
CL
K
S
L
1
CL
K
S
L
0
IOSC
Programmable Low-
Frequency Oscillator
(C8051F340/1/2/3/4/5/8/9/
A/B/C/D)
EN
EXOSC
OSCLCN
OSCLEN OSCLR
D
Y
OS
C
L
F3
OS
C
L
F2
OS
C
L
F1
OS
C
L
F0
OS
C
L
D
1
OS
C
L
D
0
n
n
OSCLF3-0