Dr. Scott M. Baker's Bubble BASIC Is a Zilog Z80-Based Single-Board Computer with Bubble Memory
Building on an earlier project to add non-volatile bubble memory storage to a Heathkit H8, this SBC is the height of 1970s technology.
Engineer Dr. Scott M. Baker has expanded his work with bubble memory technology, building a Zilog Z80-based single-board computer which uses the 1970s non-volatile storage as its working memory — and a RC2014-compatible multi-board design beside.
"I thought it would be fun to build the minimum possible computer that supported bubble memory storage, and so I developed a small Z80 computer with bubble memory, running BASIC as the programming environment," Baker explains of his latest project. "The board was easily ported to be used on the RC2014 computer."
The single-board computer Baker has created builds on his earlier work building a storage card for the Heathkit H8 microcomputer using the same bubble memory technology — originally launched in the 1970s as a non-volatile storage which operates through the migration of magnetic 'bubbles' around a patterned substrate. While the memory board simply added 128kB of storage to an existing computer, though, Baker's latest build places it at the heart of an entirely new design.
"Everyone who has designed or built a single board computer in the last decade or so has heard of the RC2014 and/or of Grant Searle’s Z80 computer," Baker notes. "The RC2014 in its most basic for is a simple Z80 computer with 32k of RAM and up to 32k of ROM. Other combinations are possible, 48k RAM with up to 16k of ROM, or even paged RAM/ROM configurations offering a megabyte or more of combined storage. RC2014s can run BASIC, CP/M, Fuzix, or a few other options. To design my single board computer, I followed a similar approach."
The resulting system uses a Zilog Z80-compatible processor, retaining compatibility with the same BASIC port as used in the RC2014, and splits the address space cleanly down the middle with 32kB of RAM and 32kB of ROM. "I actually only need about 10kB for the Bubble BASIC interpreter," Baker admits, "but it's easiest to just cut the address space in half." Elsewhere on the board is a Zilog Z8530 Serial Communications Controller (SCC), offering two serial ports and an integrated baud-rate generator, and a GAL22V10D programmable logic device for glue logic.
The bubble memory, an Intel 7110 module, acts as neither RAM nor ROM but as a readable and writable backing store for the device — offering storage for user-written programs that won't be erased when the system is shut down, and without the need to connect a tape drive, floppy disk, or other external storage device. The RC2014 variant, meanwhile, uses the same bubble memory but without the RAM, ROM, and CPU, in order to create an add-in board compatible with any RC2014 system.
Baker's full write-up is available on his website, though at the time of writing the hardware design files had not yet been uploaded to the project's GitHub repository.