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
OSC
Programmable
Internal Clock
Generator
Input
Circuit
EN
SYSCLK
n
OSCICL
OSCICN
IOSC
EN
IFRDY
IFCN1
IFCN0
XTAL1
XTAL2
Option 2
VDD
XTAL2
Option 1
10M
Option 3
XTAL2
Option 4
XTAL2
OSCXCN
XTLVL
D
XOSC
M
D
2
XOSC
M
D
1
XOSC
M
D
0
X
F
CN2
X
F
CN1
X
F
CN0
CLKSEL
C
LKSL0
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
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.
