Silicon Laboratories C8051F344 Manuel D’Utilisation

C8051F340/1/2/3/4/5/6/7 devices include a programmable internal high-frequency oscillator, a program-
mable internal low-frequency oscillator (C8051F340/1/2/3/4/5), 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.

    Clock Multiplier

OSC

Input

Circuit

XT

LVL

D

XTAL1

XTAL2

Option 2

VDD

XTAL2

Option 1

10M

Ω

Option 3

XTAL2

Option 4

XTAL2

OSCXCN

XT

L

V

LD

XO

S

C

M

D

2

XO

S

C

M

D

1

XO

S

C

M

D

0

XF

CN

2

XF

CN

1

XF

CN

0

CLKMUL

MUL

E

N

MU

LINI

T

MU

LR

D

Y

MU

LSEL

1

MU

LSEL

0

Programmable High-
Frequency Oscillator

EN

OSCICL

OSCICN

IOSCEN

IF

RDY

SUSP

END

IF

CN1

IF

CN0

EXOSC / 2

x 2

x 2

EXOSC

IOSC

SYSCLK

EXOSC

EXOSC / 2

EXOSC / 3

EXOSC / 4

IOSC / 2

USBCLK

USBC

LK2

-0

CLKSEL

US

B

C

LK

2

US

B

C

LK

1

US

B

C

LK

0

CL

KSL

2

CL

KSL

1

CL

KSL

0

IOSC

Programmable Low-

Frequency Oscillator

(C8051F340/1/2/3/4/5)

EN

EXOSC

OSCLCN

OS

C

L

E

N

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