Thank you all for your suggestions, I appreciate your help.
I'm just going to assume that the oscillator is working right.
Now the actual problem I'm facing is with the AD converter.
When I simulate the software I get the error below, I already looked the same thread on this website but they did not give the solution.
ADC-W0008: No stimulus file attached to ADRESL for A/D.
so as the warning say no stimulus is attached to address register where the a/d value is stored.so can someone explain what I'm doing wrong?
Thanks.