All of the devices in the PIC18F2X1X/4X1X family offer ten different oscillator options, allowing users a wide range of choices in developing application hardware.
These include:
? Four Crystal modes, using crystals or ceramic resonators
? Two External Clock modes, offering the option of using two pins (oscillator input and a divide-by-4 clock output) or one pin (oscillator input, with the second pin reassigned as general I/O)
? Two External RC Oscillator modes with the same pin options as the External Clock modes
? An internal oscillator block which provides an 8 MHz clock and an INTRC source (approximately 31 kHz), as well as a range of 6 user selectable clock frequencies, between 125 kHz to 4 MHz, for a total of 8 clock frequencies. This option frees the two oscillator pins for use as additional general purpose I/O.
? A Phase Lock Loop (PLL) frequency multiplier,
available to both the high-speed crystal and internal oscillator modes, which allows clock speeds of up to 40 MHz. Used with the internal oscillator, the PLL gives users a complete selection of clock speeds, from 31 kHz to 32 MHz – all without using an external crystal or clock circuit.