I want to use 14,7456 MHz xtal for my avr. I'm using ATMEGA128 in 5 Volt, for the capacitor i'm using 22pF but it looks like it's unstable. I choose the highest rising time for the fusebit and CKOPT programed. May i know some additional information about how to using high frequency xtal for the avr, about additional hardware or fusebit etc...
For this type of circuit, you want a parallel crystal, and you need to know the load capacitance the crystal is designed to operate with. This is NOT the value capacitor to build into the oscillator, but the total equivalent capacitance.
The relationship is:
CL=Cs+(C1*C2)/(C1+C2)
where CL is the load capacitance given by the manufacturer, C1 and C2 are the capacitors to ground on either side of the crystal, and Cs is the stray capacitance from the circuit board such, say 5pF or so.
Usually, C1 and C2 are chosen to be equal.
Large values of C1 and/or C2 may cause start up problems.
I want to use 14,7456 MHz xtal for my avr. I'm using ATMEGA128 in 5 Volt, for the capacitor i'm using 22pF but it looks like it's unstable. I choose the highest rising time for the fusebit and CKOPT programed. May i know some additional information about how to using high frequency xtal for the avr, about additional hardware or fusebit etc...
No, i don't have a parallel resistor with xtal. Is it necessary? In ATMEGA128 datasheet it just tell that i should use about 20-22pF for the C1 and C2 with equal value.
Anyway thanks a lot for the help.... Please help me because i can't get a stable baudrate with this xtal.