Introduced as a big brother to the 400/800 in 1982 and shipped in 1983, the
1200XL was the biggest single step forward in development of the 8-bit Atari
platform.  Innovations in comparison to the 400/800 include a full 64K of RAM
and a newly revised and expanded 16K Operating System.

The 1200XL is the only Atari to feature two LED indicator lights (L1, L2).
Normally they are both <OFF>.  L1 <ON> means the keyboard is disabled.
L2 <ON> means the new International Character Set is selected.

Keyboard enhancements introduced with the 1200XL include the new [HELP] key as
well as four programmable functions keys ([F1], [F2], [F3], [F4]).  Clicks and
system beeps output through the built-in speaker on the 400/800 are heard from
the television or monitor speaker on the 1200XL.

  1200XL Function key effects, redefinable:
     [F1] Cursor up          [SHIFT]+[F1] Cursor to upper-left corner
     [F2] Cursor down        [SHIFT]+[F2] Cursor to lower-left corner
     [F3] Cursor left        [SHIFT]+[F3] Cursor to start of physical line
     [F4] Cursor right       [SHIFT]+[F4] Cursor to end of physical line

  1200XL Function key effects, non-redefinable:
     [CONTROL]+[F1] Keyboard enable/disable (console keys unaffected)
     [CONTROL]+[F2] Screen display enable/disable
     [CONTROL]+[F3] Key click sound enable/disable
     [CONTROL]+[F4] Domestic/International character set toggle

A few features from the 400/800 are lacking in the 1200XL.  Most prominently,
the 1200XL has only 2 controller ports, and no Memo Pad mode.  Also, the
1200XL lacks the chrominance video signal on pin 5 on the Monitor port, and
lacks the +12 volts on pin 12 of the SIO port.  Furthermore, the 1200XL is the
only Atari that lacks the +5 volts on pin 10 of the SIO port.

Boot options:
   "ATARI" rainbow logo/graphics demo screen
      - Turn on computer with no cartridge inserted and no powered disk drive.
      - Press [HELP] from the "ATARI" logo screen to access Self Test program.
   Cartridge
      - Turn on computer with cartridge inserted.
   Cassette 
      1. Hold down [START] while turning on the computer.
         (System buzzer sounds.)
      2. Press [PLAY] on the program recorder.
      3. Press [RETURN] to load and run cassette program.
   Disk
      - Turn on computer with disk inserted in powered disk drive.

Box: "A Step Into the Future"

The 1200XL was only produced in an NTSC version for North America.

The 1200XL was made in the USA from January 1983 to May 1983, and in Taiwan
from April 1983 to July 1983.

By analyzing 1200XL serial numbers, Karl Heller estimates that fewer than
120,000 units total were produced, and possibly fewer than 100,000.  See the
"1200XL Owners List" thread on AtariAge:
   http://www.atariage.com/forums/index.php?showtopic=107234

Scott Stilphen mentioned this 1200XL easter egg on 10 Feb 2006:
   On 1200XLs, if you select 'all tests', when it gets to the keyboard test
   it'll type out the programmer's name.

1200XL visual tour: http://www.atari800xl.eu/public/1200xl/