Dr. Scott M. Baker's "Clover Computer" Is a Triple-Board Machine Built Atop Zilog's 16-Bit Z8000
Built around the Z8000, the Zilog Z80's considerably less popular 16-bit successor, this triple-board computer breaks the mold.
Dr. Scott M. Baker has put together a modern microcomputer built around Zilog's lesser-known 16-bit Z8000 microprocessor — after find the part while browsing an online auction site.
"I stumbled across the Z8000 on eBay one day and decided I had to go off and build myself a Z8000 single board computer," Baker explains. "I couldn’t fit it all on one board, so I figured I’d made it a two-board computer, then I figured why not add some displays and it because a three-board computer. Well, next month it’ll probably be a five-board computer!"
The definitely-not-a-single-board-computer Baker has designed uses the Z8000, Zilog's 1979 16-bit successor to the hugely successful eight-bit Z80. Lacking backwards compatibility with its predecessor and facing stiff competition from Intel's 8086 family and Motorola's 32-bit 68000 range, the Z8000 was not a commercial success — which is what makes Baker's build particularly unusual.
"The project is designed into a series of separate modules," Baker explains, "with the intention that they could be mixed and matched, and the boards small enough that they can be manufactured at a reasonable cost. A 68-bin bus connects the boards together, mostly exposing a 16-bit data bus, 20-bit address bus, and some selects for ROM and RAM."
That bus connects the three-and-counting boards together: the CPU board, which includes the Zilog Z8000 CPU itself along with clock, buffers, and glue logic; the combined memory and serial board that hosts 1MB of RAM, 1MB of flash storage, and a Z8530 serial communication controller (SCC) chip for two serial ports; and a display board, which houses eight TIL311 numerical displays and supports optional button or switch inputs.
For software, Baker turned to the popular CP/M — just recently confirmed by the current owner of its intellectual property as being fully open source and available to all, going right back to the very first versions in development at Digital. "CP/M 1.1 is used," Baker writes. "4sun5bu in his GitHub page includes a BIOS that supports IDE and the SCC. I modified this BIOS to use a flash-based disk. At some point I’ll re-enable the IDE support, and maybe add floppy support."
More details are available on Baker's website, though while the programmable logic device (PLD) files have been uploaded to GitHub Baker had not yet published schematics or board designs at the time of writing.