While cancelled in 1984, the 1090XL was an expansion box designed to add 5 expansion slots to the Atari 600XL, Atari 800XL, Atari 1400XL, and the Atari 1450XLD.  This was accomplished by connecting the Atari Computer to the 1090XL Expansion System with a 50 pin parallel cable through the Atari Computer's parallel bus.  Until it's cancellation, Atari had a prototype of several cards made for the 1090XL Expansion System and these were a 64k RAM card, an 80 column video card, a Z-80 card, and a hobbiest/prototyping card.

The 1090XL Modernized Reproduction board is an improved version of the 1090XL circuit board for the Atari 1090XL Expansion System.  This board allows you to add up to 5 expansion cards to your Atari 600XL, Atari 800XL, or Atari 130XE.  (The Atari 130XE requires, at minimum, an additional adapter board.)

This board is 100% electrically compatible with all known planned Atari expansion cards.  This board has been improved, over the original, by improving compatibility with the Atari 130XE and by improving the memory management capabilities.

Expansion cards available:

1.  80 column HDMI card using a Raspberry Pi Pico to provide XEP-80 style emulation.

2.  320k memory card that provides 64k of main memory and 256k of RAMBO compatible expanded memory.

3.  CX-85 numeric keypad card for an external CX-85 numeric keypad.

Expansion cards that have been reproduced and for which gerber files are available:

1.  64k/256k Atari Memory card.

2.  80 column video card for monochrome monitors.

3.  Prototyping/Hobbiest Card

The 50 pin parallel I/O cable is supplied.  You will need to supply the 9VAC Atari power supply.  (This is the same power supply used for an Atari 400, Atari 800, Atari 1050 disk drive, etc.)

This item is hand assembled on an as-needed basis and usually requires at least several days until it can be shipped.

The pictures show the 1090XL as follows:
2.  A reproduction 1090XL configured without the 12vdc supply and with a 320k memory upgrade card.  (The 320k memory card is not included.)

3.  The 1090XL with the 80 column card installed.  (The 80 column card is not included.)

4.  The 1090XL parallel cable's connection between the 1090XL and the Atari computer.  The 50 pin parallel cable is included.