C8051F340/1/2/3/4/5/6/7
14. Oscillators
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.
OSCICL
OSCICN
IOSCEN
IFRDY
SUSPEND
IFCN1
IFCN0
OSCLCN
OSCLEN
OSCLRDY
OSCLF3
OSCLF2
OSCLF1
OSCLF0
OSCLD1
OSCLD0
CLKSEL
USBCLK2
USBCLK1
USBCLK0
CLKSL2
CLKSL1
CLKSL0
SYSCLK
USBCLK
USBCLK2-0
Option 2
VDD
Option 3
XTAL2
XTAL2
EN
Programmable High-
Frequency Oscillator
OSCLF3-0
EN
Programmable Low-
Frequency Oscillator
IOSC
n
n
Option 1
XTAL1
10MΩ
XTAL2
(C8051F340/1/2/3/4/5)
Input
Circuit
XTLVLD
OSC
EXOSC
IOSC
EXOSC
EXOSC / 2
x2
x2
IOSC / 2
EXOSC
Option 4
XTAL2
Clock Multiplier
XTLVLD
XOSCMD2
XOSCMD1
XOSCMD0
MULSEL1
MULSEL0
MULEN
MULINIT
MULRDY
XFCN2
XFCN1
XFCN0
EXOSC / 2
EXOSC / 3
EXOSC / 4
OSCXCN
CLKMUL
Figure 14.1. Oscillator Diagram
Rev. 1.0
139
SILABS [ SILICON LABORATORIES ]
