Sjaak's Commodore SX-64 Upgrades Really Deliver on the "Executive" Promise

Mononymous maker Sjaak, also known as SMDprutser, has designed a series of upgrade boards to bring the best of modern technology to one of Commodore's most iconic machines of the 1980s: the Commodore SX-64 "Executive 64" portable.

"Several years ago, I got hold of a Commodore SX-64. Having it for so long, but now I finally came around to restore it and make it the ultimate one (for me at least)," Sjaak explains. "I didn't want to do much on the outside and [made] all the mods reversible. The stock SX64 (or C64) was very complete and it had all the original stuff (most notable the blue caps and keyboard cable), but I added several additions and 'upgrades' to it."

The Commodore SX-64 launched in 1983 as a more-or-less portable all-in-one alternative to the popular Commodore 64 line of microcomputers. Internally, its hardware was effectively the same as the Commodore 64 — but it included an integrated power supply, speaker, floppy drive, and even a five-inch cathode-ray tube (CRT) display, with a keyboard that served as a protective cover when the hefty machine was being lugged to and from the office.

Sjaak's SX-64 is entirely typical, or at least it began that way before a project to deliver considerable upgrades on add-in boards. The first of these provides a modern alternative to that iconic but ageing CRT: an equivalently-sized LCD panel, with a custom board delivering audio amplification to a new speaker. With the CRT gone, there's room for additional add-in boards: a kernel — or, using Commodore's spelling, "kernal" — switcher based on the Microchip ATmega328PB microcontroller providing on-the-fly switching between different system kernels, a custom SD2IEC board which allows the Commodore to access files on a microSD card, an speed-loader for the physical floppy drive with expanded memory, and both internal and external parallel ports.

Opening a flap that originally hid controls for the CRT display reveals another add-on, too: a custom control system, which uses two seven-segment displays to show the currently-active kernel, controls for choosing disk images from the SD2IEC board, the device ID of the internal floppy drive, and reset buttons for both the kernel version and the machine itself. Finally Sjaak added a MagicDesk cartridge, which delivers 512kB of pageable read-only memory connected direction to the machine's CPU.

Sjaak has written the project up on his website, and promises a follow-up article going into more detail about each of the add-on boards. "I also have spare PCBs of the several parts of this built," the maker adds, "[so] please drop a comment if you are interested."