About oscillator using crystal in 8051

[vudiepdh1]

Hi all i have a question about oscillator in 8051. How does it work ? There are two ceramic capacitor 33p connected to Xtal1 and Xtal2 pins . What to do ? What happen if i don't use them ? Thankss!

 

[karesz]

Hi,
check datasheet pls...
If it dont work; (depend on your IC) you can apply a parallel resistor to XTAL( pins 1 &2 , eventuell a serial rasitor between pin xtal2 & xtal with the one 33 pF to this pin. Are 33 pF not to high values_ you must check it with Quartz frequency & 51`s datasheet...
If all cannot help_buy another Xtal, possibly some other type
K.

 

[mishra12]

i don't know why 33pf is connected to gnd with crystal,but in avr series microcontroller this is not necessary.if external oscillator is selected such as ttl oscillator ,it will be connected to xtal1(19);(18)xtal2 is left unconnected .i think quartz crystal oscillator should need 33pf capacitor .

 

[karesz]

You see, AVR isnt 8051!
They are different ICs, maybe different technologys too (CMOS/Bipolar or even BICMOS), means in all situaton other input capacitances/impedances!
Your Xtal is regularly specified with a parallel C of i.e. 10--20pF!
The both capacitors an X1 & X2 are practically in serie for that: means phisically a double of value, but dont forget parasitic C`s from Board & IC!
In all YOU MUST CHECK datasheets from USED uP & XTAL!
A guessing helps not so much here:-(...
A "plus input C" is unfortunally not needed if you driv eit from external CLKosci!
K.