Oscillators And Clock Selection; Figure 21.1. Oscillator Options - Silicon Laboratories C8051T620 Manual

21. Oscillators and Clock Selection

C8051T620/1/6/7 & C8051T320/1/2/3 devices include a programmable internal high-frequency oscillator, a
programmable internal low-frequency oscillator, and an external oscillator drive circuit. The internal high-
frequency oscillator can be enabled/disabled and calibrated using the OSCICN and OSCICL registers, as
shown in Figure 21.1. The internal low-frequency oscillator can be enabled/disabled and calibrated using
the OSCLCN register. The system clock can be sourced by the external oscillator circuit or either internal
oscillator. Both internal oscillators offer a selectable post-scaling feature. The USB clock (USBCLK) can be
derived from the internal oscillators or external oscillator.
C Mode
RC Mode
VDD
XTAL2 XTAL2
Option 1
XTAL1
10M
XTAL2
CMOS Mode
XTAL2
C8051T620/1/6/7 & C8051T320/1/2/3
OSCICL OSCICN
4
EN
Programmable
2
Internal Clock
Generator
OSCLF
EN
Low Frequency
Oscillator
OSCLD
Input
OSC
Circuit
OSCXCN
CLKMUL

Figure 21.1. Oscillator Options

Rev. 1.2
OSCLCN CLKSEL
OSCLF OSCLD
n
n
Internal HFO
Internal HFO / 8
EXOSC
EXOSC / 2
EXOSC / 3
EXOSC / 4
Internal LFO
SYSCLK
USBCLK
127