PIC12F683
FIGURE 3-6:
RCIO MODE
3.4.1
INTRC AND INTRCIO MODES
VDD
The INTRC and INTRCIO modes configure the internal
oscillators as the system clock source when the device
is programmed using the Oscillator Selection (FOSC)
bits in the Configuration Word register (Register 12-1).
REXT
Internal
Clock
OSC1
In INTRC mode, the OSC1 pin is available for general
purpose I/O. The OSC2/CLKOUT pin outputs the
selected internal oscillator frequency divided by 4. The
CLKOUT signal may be used to provide a clock for
external circuitry, synchronization, calibration, test or
other application requirements.
CEXT
PIC12F683
VSS
I/O (OSC2)
GP4
Recommended values:
3 kΩ ≤ REXT ≤ 100 kΩ
CEXT > 20 pF
In INTRCIO mode, the OSC1 and OSC2 pins are
available for general purpose I/O.
The RC oscillator frequency is a function of the supply
voltage, the resistor (REXT) and capacitor (CEXT)
values and the operating temperature. Other factors
affecting the oscillator frequency are:
3.4.2
HFINTOSC
The High-Frequency Internal Oscillator (HFINTOSC) is
a factory calibrated 8 MHz internal clock source. The
frequency of the HFINTOSC can be altered approxi-
mately ±12% via software using the OSCTUNE register
(Register 3-1).
• threshold voltage variation
• component tolerances
• packaging variations in capacitances
The output of the HFINTOSC connects to a postscaler
and multiplexer (see Figure 3-1). One of seven fre-
quencies can be selected via software using the IRCF
bits (see Section 3.4.4 “Frequency Select Bits
(IRCF)”).
3.4
Internal Clock Modes
The PIC12F683 has two independent, internal oscilla-
tors that can be configured or selected as the system
clock source.
The HFINTOSC is enabled by selecting any frequency
between 8 MHz and 125 kHz (IRCF ≠ 000) as the
system clock source (SCS = 1), or when Two-Speed
Start-up is enabled (IESO = 1and IRCF ≠ 000).
1. The HFINTOSC (High-Frequency Internal Oscil-
lator) is factory calibrated and operates at 8 MHz.
The frequency of the HFINTOSC can be user
adjusted ±12% via software using the OSCTUNE
register (Register 3-1).
The HF Internal Oscillator (HTS) bit (OSCCON<2>)
indicates whether the HFINTOSC is stable or not.
2. The LFINTOSC (Low-Frequency Internal
Oscillator) is uncalibrated and operates at
approximately 31 kHz.
The system clock speed can be selected via software
using the Internal Oscillator Frequency Select (IRCF)
bits.
The system clock can be selected between external or
internal clock sources via the System Clock Selection
(SCS) bit (see Section 3.5 “Clock Switching”).
DS41211B-page 22
Preliminary
2004 Microchip Technology Inc.
MICROCHIP [ MICROCHIP ]
