research here:
http://www.geocities.com/SiliconValley/Vista/3015/atari65xem.html
and here:
http://www.backntime.net/Atari%20Computers/8bit/Prototype/Frame8bitProto.html
and here:
http://www.pipeline.com/~jhardie/
and many, many more...just do a search on Google.com for Atari 65xem