crystal oscillator 8051

why in some micro controller one pin of crystal oscillator is left unconnected. overall the question is what is the role and application of the two pin of crystal oscillator .

Hi,

Show the circuit you are taking about.

Klaus

sir,
you can refer the basic 8051 pin connection ,where pin 18 and 19 both are used for oscillator circuit connection.
In what condition one out of the two pin left unconnected.

XTAL1 and XTAL2 have an inverting amplifier between them. I you connect a crystal across them and add loading capacitors to ground it forms an oscillator at XTAL frequency.

If you want to use an external oscillator (clock) source, ground XTAL1 and drive a square wave in at XTAL2 instead.

It is all explained, in writing and diagrams in the data sheet.

Brian.