Crystal or oscillator

[pulsar.nova12]

When you create a project you can choose crystal or oscillator, what is the difference between both ?

[Ttelmah]

A crystal, is just what it says. A crystal fitted across two pins of the chip. These pins internally have an inverting gate, that then makes it oscillate.
The external oscillator, is a complete module including the drive electronics, that oscillates and generates a clock signal. This single signal can then be fed into one pin on the PIC. You can then elect to use the second pin for either logic I/O, or as a clock output to drive other circuitry.

So the first plus for the external oscillator, is that it only needs one pin.

Then most have sufficient output drive, that the same signal can be used to drive other circuitry.

Then you can also get modules that perform far better than the simple crystal. So a good crystal will give perhaps 50PPM tolerance. You can get external oscillator modules that include their own temperature compensation, and give much better accuracy. 2PPM is quite common, and 0,5PPM is readily available.

The crystal needs more careful layout, requires the right loading capacitance, but is generally cheaper, but the prices of TCXO modules have plummeted in recent years with the increasing needs for highly accurate oscillators, and are now often little more expensive than the crystal.

[temtronic]

I would like to add that an 'oscillator' does require power, so be sure to check it's specs before using especilly on battery powered projects !
The more accurate ones use more power than the 'regular' ones.
Just something to consider....

Jay