The function of an oscillator circuit is to provide an accurate and stable periodic clock signal to a microcontroller. The frequency of this clock signal can range from a few kilohertz to tens of megahertz and determines how quickly the microcontroller executes its instructions.

Most microcontrollers include a clock driver circuit which is designed to drive a quartz crystal into oscillation. The clock driver circuitry built into the PICmicro family is very flexible and allows for four different clocking options: clock signal supplied from another oscillator, an R-C clock (based on a resistor-capacitor charging time constant), a ceramic resonator, or a crystal oscillator.

Building the Oscillator

A few general precautions should be observed when building the oscillator circuit. Since the clock oscillator is typically the source of the fastest signals, and potentially, the major source of RF emissions in a circuit, good design practice dictates that all clock circuit signal lengths should be kept
as short as possible. A good, low impedance ground return wire from
capacitors C1 and C2 to the circuit ground is also necessary.

Some PICmicros, like the PIC16C711, use the pins adjacent to the clock oscillator circuit as analog inputs. For accurate analogto-digital conversion it is especially important to minimize the length of any clock oscillator signal wires running in parallel with the analog input lines. Ideally, separate the analog signal lines from any digital signals by using a ground wire as a shield between all analog and digital wiring.

Also Read: Multi Wave Oscillator, Crystal Oscillator, Voltage Controlled Oscillator, Colpitts Oscillator, Oscillator Circuit, Mcclellan Oscillator, Clock Oscillator, Hartley Oscillator