1088XEL/1088XLD Ultimate 1MB Firmware

In January 2017, Michael St Pierre (mytek) embarked on the project he’d been contemplating for two years: a completely redesigned Atari 8-bit motherboard, with an Mini-ITX form factor and using the original VLSI chips. After only nine months of gestation, the fully debugged version 1.1 boards arrived.

From the outset, the 1088XEL was built around the TK-II, Mousetari, UAV and Ultimate 1MB. Having already seen and used my alternative Ultimate 1MB firmware, Michael soon invited me to become involved in the 1088XEL testing process and asked if I could customise the BIOS in order to support the new motherboard’s unique features. Of course, the new firmware’s plug-in architecture made the creation of a drop-in 1088XEL module easy, although as time went on, a few modifications to the base code were also made.

Eventually, customised versions of the U1MB main BIOS, PBI BIOS and XEX loader were developed for the 1088XEL. Some changes – such as support for dual physical disks (used with the XEL-CF adapter) – proved highly challenging, but by the close of 2017, the new firmware was taking shape, although bug fixing and further development of the 1088XEL continued until April 2018. As the firmware neared completion. the task of updating the user manual and technical documentation began. By the beginning of June 2018, everything was finally completed.

In July 2018, Michael tabled the idea of another new Atari 8-bit motherboard, this time to be housed in a 1050 disk drive case. The result was the 1088XLD.

The 1088XEL and 1088XLD share almost identical Ultimate 1MB firmware, aside from the branding of the main BIOS. You should download the firmware which corresponds to your hardware.

New to Version 4.2

  • SIDE3 Loader-style menu design
  • Fixed Sophia 2 plugin
  • Fixed JED version reporting

Firmware Download

1088XEL U1MB Firmware 4.2 (24 January 2023)

1088XLD U1MB Firmware 4.2 (24 January 2023)

Important: Owners of Ultimate 1MB with the original v.1 CPLD code from Candle’s first run of boards (with glossy black PCB and requiring current limiting resisitors on the MMU cable) must ensure that they update to the current JED prior to installing the new BIOS, otherwise they risk bricking the device. Boards with the PBI feature (including all manufactured by Lotharek and those from Candle’s second run) will safely run the new BIOS without modification. If your U1MB has a white PCB or was purchased new from a commercial vendor since 2013, it is guaranteed to be compatible with the new firmware.


Be sure to download the toolkit ATR which includes several utilities and drivers not included in the SDX ROMs:


User Manual

The User Manual contains installation instructions and usage notes for the Main BIOS setup utility and XEL Loader:

Ultimate 1MB, Incognito, 1088XEL/XLD, SIDE Firmware Manual

Loader Quick Reference

Technical Documentation

Technical documentation describing the firmware memory map, configuration data layout and Plugin architecture is provided below:

Ultimate 1MB, Incognito and 1088XEL-U1MB BIOS Technical Documentation

Plugin Source Code

To complement the Technical Documentation, you can also download the source code for the U1MB BIOS plugins:

Ultimate 1MB BIOS Plugin Source Code

Previous Versions

1088XEL Links

To learn more about the 1088XEL and 1088XLD projects, please visit the 1088XEL home page and the 1088XLD home page, where you’ll find links to schematics, Gerbers, PIC firmware, and documentation.

As well as the 1088XEL and XEL-CF, Michael offers many other interesting projects at AtariBits.

If you’d like to purchase 1088XEL in ready-built or kit form, you can find ordering instructions at The Brewing Academy.

Licensing and Donations

While the firmware is free at the point of delivery for personal use, if it is to be included on commercially sold devices, the firmware is subject to a licensing fee which should be arranged with the author in advance. Developers interested in customised versions of the firmware tailored to their particular hardware should contact the author.

In light of the fact that firmware licensing revenue is modest and that updates are offered for free to the end user, donations are welcomed and appreciated. Indeed, it has been my mission to facilitate easy and safe firmware updates, and regular in-the-field upgrades are encouraged to ensure that devices remain up to date and bug fixes are delivered in a timely manner.

Thank you!