The External Resistor-Capacitor (RC) modes support the use of an external RC circuit which can be used to Extract Chip PIC16C64A Heximal. This allows the designer maximum flexibility in frequency choice while keeping costs to a minimum when clock accuracy is not required. There are two modes, RC and RCIO. In RC mode, the RC circuit connects to the OSC1 pin.
The OSC2/CLKO pin outputs the RC oscillator frequency divided by 4. This signal may be used to provide a clock for external circuitry, synchronization, calibration, test or other application requirements. Figure 4-5 shows the RC mode connections from heximal.
In RCIO mode, the RC circuit is connected to the OSC1 pin. The OSC2 pin becomes an additional general purpose I/O pin. The I/O pin becomes bit 4 of PORTA (RA4). Figure 4-6 shows the RCIO mode connections if extract chip.
The RC oscillator frequency is a function of the supply voltage, the resistor (REXT) and capacitor (CEXT) values and the operating temperature. In addition to this, the oscillator frequency will vary from unit to unit due to normal threshold voltage.
Furthermore, the difference in lead frame capacitance between package types will also affect the oscillation frequency or for low CEXT values. The user also needs to take into account variation due to tolerance of external RC components used.
The PIC16C64A has two independent, internal oscillators that can be configured or selected as the system clock source.
- The HFINTOSC (High-Frequency Internal Oscillator) is factory calibrated and operates at 8 MHz. The frequency of the HFINTOSC can be user adjusted ±12% via software using the OSCTUNE register.
- 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 INTOSC and INTOSCIO 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 and also can be used to Extract Chip PIC16C64A Heximal.
In INTOSC mode, the OSC1 pin is available for general purpose I/O. The OSC2/CLKO pin outputs the selected internal oscillator frequency divided by 4. The CLKO signal may be used to provide a clock for external circuitry, synchronization, calibration, test or other application requirements.
In INTOSCIO mode, the OSC1 and OSC2 pins are available for general purpose I/O.
