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A project log for MC68000 Computer

BenchoffBenchoff 12/20/2013 at 23:190 Comments


Have we said Hackaday’s evil corporate overlords are really cool recently? They are. They really, really are. They’re so cool, in fact, that they want some more original content for Hackaday. One conversation leads to another, and they’ve greenlighted yet another new project: the development of a homebrew computer, based on the Motorola 68000 processor.

So what, you may ask. There are plenty of homebrew projects around: [Quinn Dunki] is building an awesome 6502 computer named Veronica, Z80-based computers are a dime a dozen (example 1, 2, and 3). A project using a true 16-bit CPU is rare, though. We featured a few homebrew 68000 computers a while back but short of those, an awesome 65816 build, and [Jeri Ellsworth]’s awesome C-ONE computer, we haven’t seen very many homebrew projects break the 8-bit barrier.

This project aims to fix that. Every few weeks, I’ll be posting the recent developments in the construction of a 68k computer. I’m sure you all want a high-level overview of what this project entails, so here we go:

Designed around a backplane

While not the best for very high-speed circuits, I’ll be building this computer around a backplane for several reasons. First, it allows me to build the computer in a piecemeal fashion. First the power, reset, clock, and CPU modules, then a serial interface, a huge amount of RAM, and finally some sort of video output and a hard drive of some sort. Secondly, it just looks cool.

Wire-wrapped prototypes.

Eagle and KiCAD are all the rage with the kiddies these days, but PCBs have a turnaround time that’s just too long for me. Yes, I could etch my own boards just like [Quinn Dunki] does for Veronica, but wire wrapping, done correctly, is a method that just doesn’t fail. Solderless breadboards are out of the question, because eventually I’ll be lugging this around to Makerfaires and the like.

A ludicrous amount of RAM and Gigabytes of storage

8-bit CPUs generally have a 16-bit address space, limiting them to 64 kilobytes of RAM without bank switching. The 68000 has a 24-bit address space, meaning it can access 16 Megabytes of RAM. Of course I’ll need some of that space for ROM and I/O devices, but this computer will have 4 Megabytes of RAM. While I’m at it, I might as well work out an IDE interface so CompactFlash cards can be plugged in and accessed. Yes, a solid state boot drive. It’s like living in the present.

A UNIX-ish OS and a C compiler.

This is what the 68000 was designed to do. Even though the 68000 found its way into the original Macintosh, Amigas, the Sega Genesis, and a million arcade boards, some of the most advanced applications for the 68k were in Unix workstations. I won’t be able to run a complete version of UNIX as the 68k doesn’t have a memory management unit (I’d have to move up to a 68020 for that), but I can get close.

Peripherals

Ethernet? Oh yeah. The 68000 easily has all the power to run a TCP stack and get on the Internet.

Yes, it’s somewhat of an ambitious project. Hackaday needs a way to show off the new Projects thing, though, and I was going to build this anyway.

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