Atari's Classic 600XL, 800XL Gain CP/M Support with This 1090 XL Zilog Z80 Expansion Board

Based on long-forgotten designs from Atari itself, this expansion card offers support for a work-in-progress CP/M port.

Gareth Halfacree
1 month agoRetro Tech

Pseudonymous maker and vintage computing enthusiast "reifsnyderb" has brought a long-forgotten piece of Atari history back to life, creating a modern version of an ultra-rare Atari 1090 XL Expansion System board that adds a Zilog Z80 CPU and Digital CP/M compatibility — though describes software support as being a work-in-progress.

"In 1984, there is extensive evidence that Atari designed two CP/M Z80 cards for the 1090XL," reifsnyderb explains. "One of these cards was a non-functional prototype and one may still exist. A schematic diagram exists of the other card. The discovered software appears to work with the card version for which only a schematic diagram remains. This card is a full-size updated version, in a classic styling, with 64k of on-board memory. It's function is based upon the schematic of the second card."

The Atari 1090 XL Expansion System launched in 1983 as an optional accessory for the Atari XL 600XL and 800XL home computers, offering the ability to connect multiple expansion boards to a single system. These could range from simple memory expansions to the Atari 1066, which was to add a Zilog Z80 CPU and compatibility with Digital's CP/M operating system to the MOS Technology 6502-based XL range.

The board reifsnyderb has created is as close a recreation to the Atari 1066 as possible, though it includes 64kB of on-board memory rather than relying on the Atari XL's own internal memory. As with Atari's original design, it hosts a Zilog Z80 CPU running at at least 8MHz — and provides support for an early port of CP/M, which its creator describes as being in "an alpha state of development."

The 1090 XL Z80 CP/M card has been listed on reifsnyderb's Tindie store at $99.95, excluding the recently-discontinued Zilog Z80 CPU required to make it run; details on its development are available in the project's Atari Age forum thread. The card was out of stock at the time of writing, with reifsnyderb suggesting more cards will be available the week commencing June 10th.

Gareth Halfacree
Freelance journalist, technical author, hacker, tinkerer, erstwhile sysadmin. For hire: freelance@halfacree.co.uk.
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