About a year ago I had a look at my collection of Commodore 64 floppies and decided that it was time, enough time had passed that even I needed to look into backing them up - hoping simply doesn't cut it in the end. I had a look at the available options, then instead of just choosing to buy something like the ZoomFloppy I wanted to build it myself. With the resources available to me online, all of the heavy lifting was already done. The work of transferring the designs to PCB using KiCAD resulted in the previous version, creatively called C64 XUM1541. Now that a year has gone by, mostly isolated like most of the world I wanted to make a new revision with few tweaks and so I made the C64 XUM1541-II.
What had somewhat annoyed me that the C64 XUM1541 was its apparant limition when it came to running anything past version 0.7 of the OpenCBM firmware, so I finally got around to actually reading the documentation that came with it. I don't know the exact point in time the designs parted ways, but thinking practically - I instead just focused on making a version of it that would work. Mostly by adding the components required for the 7406-version of the reference design included with OpenCBM.
Not quite substantial enough to warrant documenting them as separate projects, I've also taken a look at implementing some of the simpler upgrades for the Commodore 1541-II as they are the type of drives I have available. Read through the included documentation before attempting to perform any of the upgrades as well as ensuring that they actually fit into the drive you have.
The following modules are available as part of this project. The additional modules are strictly not necessary as you can simply use the C64 XUM1541-II by itself with a drive, the parallel interface will cut the time needed to backup a single disk in half. The remaining modules mainly just affect your experience when using the drive with your physical Commodore 64, but note that most of them have been designed for use with a Commodore 1541-II disk drive. The SpeedDOS user port adapter has been included for completeness, but before getting excited about the possiblities you should be aware that the speed gains will probably be less than what you'd obtain by simply installing JiffyDOS in your disk drive as well as the computer itself.
The following table lists all of the modules, click the name to get a more detailed description as well as other information for that specific module. The second and third column has been added to show which module can be used with each other, the 'XUM1541' giving a recommendation when performing backups on a modern computer. The third column provides a recommendation when you want to use the modified drive with your physical Commodore 64.
| Module | C64 XUM1541-II | Physical C64 | Order | Description |
|---|---|---|---|---|
| C64 XUM1541-II | required | N/A | PCBWay | C64 XUM1541-II module for backing disks up to modern computer. |
| C64 XUM1541-II Faceplate | optional | N/A | PCBWay FA1 | Optional faceplates suitable for installing on top of C64 XUM1541-II, hiding away most of the electronics in a way that would mimic a case with a minimal amount of work. |
| C64 1541-II VIA Adapter | recommended | optional | PCBWay | Adds a parallel interface to your Commodore 1541-II disk drive, can be used with both C64 XUM1541-II as well as physical computer with a suitable ROM upgrade. |
| C64 1541-II ROM Adapter | optional | recommended | PCBWay | Adds a switch to select between ROM images suitable for Commodore 1541-II disk drive with only a single 16KB ROM chip. |
| C64 SpeedDOS Adapter | N/A | optional | PCBWay | User port adapter for connecting a 1541-II disk drive with a parallel cable up to your Commodore 64, requires matching firmware on the drive as well as the computer. |
| C64 Kernal Switcher | N/A | recommended | PCBWay | Using a custom kernal with optimizations for either serial or parallel interfaces is recommended. This board was designed for use with C64 "Longboards". |
Building an XUM1541 from scratch and getting the software ready to transfer your own physical disks, is a rather involving process. It is an afternoons worth of a project, but by following the documentation it shouldn't be a difficult task for anyone equipped with a brain for slight engineering. As the project really is just a collection of various modules that you may or may not need, I've separated the information so that the relevant documentation is included as a separate README for each of the modules - click the module name for BOM, build instructions and so forth.
When you're ready to start installing software, by first installing the firmware onto the Arduino Pro Micro and then installing OpenCBM, there's a separate document covering these details: