C8051F310 datasheet(121/228 Pages) SILABS

121 / 228 page

Rev. 1.7

121

C8051F310/1/2/3/4/5/6/7

12. Oscillators

C8051F31x devices include a programmable internal oscillator and an external oscillator drive circuit. The

internal oscillator can be enabled/disabled and calibrated using the OSCICN and OSCICL registers, as

shown in Figure 12.1. The system clock can be sourced by the external oscillator circuit, the internal oscil-

lator, or a scaled version of the internal oscillator. The internal oscillator's electrical specifications are given

in Table 12.1 on page 123.

Figure 12.1. Oscillator Diagram

12.1. Programmable Internal Oscillator

All C8051F31x devices include a programmable internal oscillator that defaults as the system clock after a

system reset. The internal oscillator period can be programmed via the OSCICL register as defined by

SFR Definition 12.1 OSCICL is factor calibrated to obtain a 24.5 MHz frequency.

Electrical specifications for the precision internal oscillator are given in Table 12.1 on page 123. Note that

the system clock may be derived from the programmed internal oscillator divided by 1, 2, 4, or 8, as

defined by the IFCN bits in register OSCICN. The divide value defaults to 8 following a reset.

OSC

Programmable

Internal Clock

Generator

Input

Circuit

SYSCLK

OSCICL

OSCICN

XTAL1

XTAL2

Option 2

VDD

XTAL2

Option 1

10M

Ω

Option 3

XTAL2

Option 4

XTAL2

OSCXCN

CLKSEL

C8051F310 Datasheet(PDF) 121 Page - Silicon Laboratories