Thomas Christoph of COREi64 has done it again, completing a thorough reverse engineering project for the CMD 1750XL 2MB REU. For those unfamiliar, the 1750XL is an expanded memory unit designed for the Commodore 64 and 128, offering significantly more storage for users pushing the limits of these classic systems.
The project’s goal was clear from the start: recreate the original CMD 1750XL using the 64-pin DIP version of the 8726 REC chip, while also offering a variant compatible with the PLCC version of the same chip. Now, both designs are finalized and fully operational. Christoph’s recreation maintains the functionality of the original REU, with an added focus on making the design accessible to modern enthusiasts.
The real challenge lies in distribution. The 8726 REC chip, essential for the REU’s functionality, isn’t widely available. Christoph suggests a practical approach for users: repurpose chips from existing Commodore REUs like the 1700, 1750, or 1764. This method enables enthusiasts to build their own CMD 2MB REU without relying on an external supply of chips.
Christoph has opened the floor for input on how to move forward. Options include:
- Bare PCBs: Providing just the circuit boards and GAL chips, leaving the soldering and assembly to users.
- Partially Assembled Units: Offering soldered boards requiring users to install their own 8726 REC chip.
- Complete Units (Without REC Chip): These would include a pre-assembled board housed in an original Commodore case. Christoph’s supply of original cases is limited to a handful of units, so this option is reserved for a lucky few.
- Reproduction Cases: Christoph is prepared to design and produce new cases compatible with the board if demand continues.
Community feedback will guide the next steps, determining which formats are most useful and accessible. By prioritizing modularity and DIY possibilities, Christoph’s work ensures this piece of Commodore history remains within reach of everyone.
