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The LP, XT and HS modes support the use of quartz crystal resonators or ceramic resonators connected to OSC1 and OSC2 (Figure 3-3). The mode selects a low, medium or high gain setting of the internal inverter amplifier to support various resonator types and speed.
LP Oscillator mode selects the lowest gain setting of the internal inverter-amplifier. LP mode current consumption is the least of the three modes. This mode is designed to drive only 32.768 kHz tuning-fork type crystals (watch crystals) if extract pic16f716 microcontroller flash.
XT Oscillator mode selects the intermediate gain setting of the internal inverter-amplifier. XT mode current consumption is the medium of the three modes. This mode is best suited to drive resonators with a medium drive level specification.
HS Oscillator mode selects the highest gain setting of the internal inverter-amplifier. HS mode current consumption is the highest of the three modes. This mode is best suited for resonators that require a high drive setting.
The external Resistor-Capacitor (RC) modes support the use of an external RC circuit. 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 OSC1. OSC2/ CLKOUT 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 3-5 shows the external RC mode connections if read copy pic16f627a microcontroller flash.
In RCIO mode, the RC circuit is connected to OSC1. OSC2 becomes an additional general purpose I/O pin. 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:
- threshold voltage variation
- component tolerances
- packaging variations in capacitance
The user also needs to take into account variation due to tolerance of external RC components used. The Oscillator module 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 via software using the OSCTUNE register.
- The LFINTOSC (Low-Frequency Internal Oscillator) is uncalibrated and operates at 31 kHz.
