Atari* System Reference manual
    
                (c) 1987 By Bob DuHamel
     
 
                      Bob Duhamel
                 6915 Casselberry Way
                 San Diego, CA  92119


                                                                          


     This manual contains highly technical information.  Such information
     is provided for those who know how to use it.  To understand the
     advanced information you are expected to know 6502 assembly language. 
     If you are new to programming, concentrate on the parts which discuss
     BASIC commands.
     
     Addresses are usually given in both hexadecimal and decimal numbers. 
     The operating system equate names are given in capital letters with
     the address following in brackets.  The decimal address is in
     parenthsis within the brackets.  For example:
     
      DOSVEC [$000A,2 (10)]
     
      name     hex     dec
     
     The ",2" after the hexadecimal number means that this address requires
     two bytes to hold its' information.  Any address called a "vector"
     uses two bytes whether noted or not.
     
     Control registers and some other bytes of memory are shown in the
     following format
     
                                Register format
     
           7 6 5 4 3 2 1 0
          -----------------
          |               |
          -----------------
           1 6 3 1 8 4 2 1
           2 4 2 6
           8
     
     The numbers on top are the bit numbers.  Bit 7 is the Most Significant
     Bit (MSB) and bit 0 is the Least Significant bit (LSB).  The numbers
     on the bottom are the bit weights.  These are useful when changing
     memory with decimal numbers, as you would in BASIC.  For example, to
     set bit 4 of a register to 1, without changing any other bits you
     would add 16 to the decimal number already in the register.  To reset
     the same bit to 0, you would subtract 16 from the number in the
     register.  This is exactly what the command GRAPHICS 8+16 does.  It
     sets bits 3 and 4 of a graphics mode control register.
     
     MSB and LSB may also mean Most Significant Byte or Least Significant
     Byte, depending on context.