As Abhishek said, you can generate a square wave and add wave-shaping circuits at the output pin to derive different waveforms. we have had several discussions on such circuits before on this forum. However, it's is probably easier to do it all using software and a DAC.

Also instead of making the waveform frequency dependent on your crystal, you could control that programmatically too, using timers and interrupts. It is not too difficult to do. In fact you can even move on to variable duty cycle waveforms!

kundi