AVR-Chat

Hi all,

I have been looking at PICs and the Atmel chips and the major 
difference appears to be that PIC has one major category and all the 
parts are slightly different.

It seems that you cannot write a program on a PIC and then just port 
it to any other pic.  In some cases, it needs major work, in others, 
its just a few changes.  I think that has a lot to do with the memory 
and how that works.

The Atmel chips are supposed to offer a much better upgrade or should 
I say, chip family ?

The idea being that if you write a program for one chip, you can 
upgrade to another in the same family with very little difficulty.

Anyway, while looking for programmers, I was shown a like to a 
developemnt board and found controller boards.  Herein lies he 
question.

There are ATmega chips, AVR chips, ATmini chips, AT90 chips.

Are these pretty seperate families ? by that I mean if one writes for 
an AT89, do all AT89 chips pretty much use the same program ?  or 
would one need to re-write more than just a few lines to make it 
work ?

Can one write for the ATmini and then use that program on the AT90 ?

I have been googling things like 'differences in atmel chips' 
or 'difference between atmini and avr' and am not getting answers.

Any enlightenment would be appreciated.

Dave