Most retrocomputer builds seem to focus on either restoring old machines or rebuilding them from scratch. Either way, the goal is to get as close as possible to the original machine, and while we certainly respect those builds, there are other ways to celebrate the computers of yesterday, as this Z80 single-board computer nicely demonstrates.
[Ivan Farafontov]’s SBC is sort of a “Z80 that never was” build, one that would almost have been possible back in the heyday of 8-bit computing, and would have made quite a splash if it had. Most of the peripheral chips are from Zilog and would have been found in many of the Z80 machines of the day, like the TRS-80 and ZX Spectrum. Where it goes off the old-school path is with the video section, which uses an Atmel CPLD chip and a dual-port RAM to drive a VGA monitor. It still looks the part, though, with a 256×192 pixel, 16-color display. The compact video section helps keep the overall footprint of this machine pretty small, at least by the standards of the old machines. The machine is barely larger than its custom keyboard, which is populated with mechanical switches and really nice-looking custom keycaps, and everything fits into a 3D-printed case.
The demo that starts at the 4:30 mark of the video below will be a nostalgia storm for a lot of readers, starting as it does with a version of Boulder Dash that [Ivan] wrote from scratch, along with the tile editor he used to create the sprites for the game. All the design files and code are available if you want to build your own, of course. We recently featured another Z80 that never was, but [Ivan]’s machine really makes a statement with its compact size and its capabilities.
Given the era, the CPLDs would need to be merged into an ASIC.
In the second half of the 1980’s this could have been done with off-the-shelf components on a 2-layer PCB roughly the same size (except RAM chips). Using HD64180 and µPD7220 no fancy CPLDs or ASICs were needed, just some PALs or 74xx.
Of course, but it still means that it would be completely doable using period tech.
don’t you mean an ULA ?
Could an Uncommitted Logic Array by Ferranti have been an option, if it were a production design back in the day?
That’s when i started my chip design career. Out depends what was in the CPLD; if it’s just address decode, a ULA would have been ideal.
Even with the ASIC, would have had to wait a few years for a VGA monitor.
Since the late 1970s, color monitors with analog RGB inputs were available in most parts of the civilized world. We called them “TV sets”.
Great project. Just wondering if there is a limitation on the graphics resolution? Something like a 80 x 25 text mode?
Looking at the board schematics, the video CPLD is already clocked at 25MHz i.e. 640×480 VGA video timing, meaning 80 x 25 character monochrome text mode should be theoretically possible with the current circuit. Worst case, one might need to up VGACLK to 50MHz, extend the x-axis pixel counter in the CPLD to 10 bits instead of 8 and other CPLD-related tweaks.
Going to a 75MHz VGACLK might even be able to yield a 16-color 80×25 text screen, possibly.
Also yes, his computer remind me of the Vtech Laser 300 system I had as a kid growing up in the 80’s – only his machine is potentially a lot more capable! 🙂
32bits diy home computer soon with fullhd display?
I love “What if” projects like this.
But does it run Cry.. err, MP/M II ? 🙂
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