C8051T602-GS View Datasheet(PDF) - Silicon Laboratories
Part Name
Description
MFG CO.
'C8051T602-GS' PDF : 168 Pages View PDF
C8051T600/1/2/3/4/5/6
21. Oscillators and Clock Selection
C8051T600/1/2/3/4/5/6 devices include a programmable internal high-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 system clock can be sourced by the
external oscillator circuit or the internal oscillator (default). The internal oscillator offers a selectable post-
scaling feature, which is initially set to divide the clock by 8.
OSCICL
OSCICN
RC Mode
VDD
EXTCLK
EN
Programmable
Internal Clock
n
Generator
C Mode
EXTCLK
EXTCLK
Input
Circuit
OSC
SYSCLK
CMOS Mode
EXTCLK
OSCXCN
Figure 21.1. Oscillator Options
21.1. System Clock Selection
The CLKSL bit in register OSCICN selects which oscillator source is used as the system clock. CLKSL
must be set to 1 for the system clock to run from the external oscillator; however the external oscillator may
still clock certain peripherals (timers, PCA) when the internal oscillator is selected as the system clock. The
system clock may be switched on-the-fly between the internal oscillator and external oscillator, as long as
the selected clock source is enabled and running.
The internal high-frequency oscillator requires little start-up time and may be selected as the system clock
immediately following the register write, which enables the oscillator. The external RC and C modes also
typically require no startup time.
100
Rev. 1.2
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