C8051F02X Datasheet, PDF (135/272 Pages) Silicon Laboratories – 8K ISP FLASH MCU Family

C8051F020/1/2/3
14. OSCILLATORS
Each MCU includes an internal oscillator and an external oscillator drive circuit, either of which can generate the sys-
tem clock. The MCUs operate from the internal oscillator after any reset. This internal oscillator can be enabled/dis-
abled and its frequency can be set using the Internal Oscillator Control Register (OSCICN) as shown in Figure 14.1.
The internal oscillator's electrical specifications are given in Table 14.1.
Both oscillators are disabled when the /RST pin is held low. The MCUs can run from the internal oscillator perma-
nently, or can switch to the external oscillator if desired using CLKSL bit in the OSCICN Register. The external oscil-
lator requires an external resonator, crystal, capacitor, or RC network connected to the XTAL1/XTAL2 pins (see
Table 14.1). The oscillator circuit must be configured for one of these sources in the OSCXCN register. An external
CMOS clock can also provide the system clock; in this configuration, the XTAL1 pin is used as the CMOS clock
input. The XTAL1 and XTAL2 pins are NOT 5V tolerant.
Figure 14.1. Oscillator Diagram
OSCICN
opt. 4
XTAL1
opt. 3
XTAL1
XTAL2
opt. 2
AV+
XTAL1
opt. 1
XTAL1
XTAL2
VDD
EN
Internal Clock
Generator
AV+
Input
Circuit
OSC
AGND
OSCXCN
SYSCLK
Rev. 1.4
135