avr +selecting external crystal problem

i am using stk200/300 programmer for programming my atmega8 avr(my software is bascom 1.11.7.4)
in one of my program i used the internal 8M oscillator and i don`t have
any problem with it but in another program i need external 16M crystal to
work. so i defined the CKSEL t0 1111 and write the fusebit on the avr and then i placed
the 16M crystal on pin no. 9&10 of atmega8 but when i started to write my program on a chip
the programmer couldn`t identify my chip.
i used another atmega8 and before changing the internal oscillator to external crystal
i placed the 16M crystal on pin no. 9&10 of atmega8 and then i changed the oscillator
to external crystal and write the fusebits on it . this time also when i started to
write the program on my chip strangely my programmer couldn`t identify the chip another
time .
what do you think about this problem ?
please help me.

dont forget you need some other param when chage os xtal frq in Avr check Datashheet for more detail

also L version of some AVRhave max clock of 8 mhz also ....

the max freq of the atmega8 that i am using is 16M(atmega8-16pu) ?!!!
and plz let me know what are other parameters ?

clockselect 1010
to have noise immunity ckopt=0
slowly rising power

What's the capacitors you are using with 8M and 16M crystal?
For higher freq. crystal, the cap value should be smaller.

Also can you verify if the crystal is a serial cut or paralle cut? Those are different types and require differnt driver circuits.

Driving the microcontrollers at its maximum speed is not advisable

have you tried it with lower speeds

regards
Nandhu

Check capacitors.

I think it might be the problem due to capacitors, choose the accurate value of capacitor. See whether your chip is atmega8 or atmega8l and have capacity to drive to that much frequency


Bibin John
www.bibinjohn.tk