I picked up an Atari 800XL today and it came with a double sided Programmers Aid for Atari Computers. I just play the games and don't dabble in programming. It is dated 1982. If anyone is interested, I will gladly email the information contained on this. Just send me a message or reply to this post. Long live FREEdom of information! It has 18 sections for:
Basic Keywords
Musical Notes and Pitch Values
Error Messages
Atari Hues
Joystick
Operators
Default Colors
Mode/Color Table
Antic Modes and Screen Formats
Antic Blank-line Opcodes
Antic Instruction Modifiers
Connector Pinouts
Free Ram in Page Zero
Free Ram Elsewhere
Operating System Entry Points
Floating Point ROM Entry Points
Important Memory Locations -- RAM
Important Memory Locations -- Hardware Registers