Homebrew 68k Extravaganza

Introduced in 1979, the Motorola 68000 CPU was first used in very expensive and very high-end workstations from the likes of Sun and SGI. As the processor matured it became well-known for its use in the original Macintosh, early Amigas, and even the TI-89 graphing calculator and a few video game consoles such as the Sega Genesis and Atari Jaguar.

A few days ago when I posted a homebrew computer build based on the 65816 CPU, I lamented the lack of builds using the venerable Motorola 68k. Hackaday readers were quick to point out the many homebrew computers making use of this classic CPU, and I’m glad to post them here.

First up is an amazing 68008 build featuring an IDE disk interface, a floppy disk interface, 10base-T Ethernet connectivity, a real-time clock, and two SID synthesizer chips. As far as features go, this build takes the cake. Pity I can’t find a writeup.

Here’s a 68000-based computer built around the S-100 bus. Like the first computer to use the S-100 bus, the Altair 8800, this computer is plugged into a backplane that breaks out the data, address, and interrupt lines to every device on the bus.

Of course, no mention of backplane computers would be complete without a Eurocard version. [N8VEM] built a 68000 computer able to be plugged in to a backplane along with an IDE controller card and a display controller.

Finally, in true ‘giant mess of wires’ spirit, [Dajgoro] sent in his 68k single board computer featuring 512 kB of RAM and a 16k ROM. [Dajgoro] also took the time to wire in a PIC microcontroller, allowing him to expand his computer far beyond what vintage components would allow.

The 68k was – and still is – a very powerful CPU that far surpasses the capabilities of the 6502 and Z80 homebrew computers we see from time to time. Short of building a 486 or Pentium-based computer from scratch, building a 68k machine is one of the crowning achievements of hardware hackery, and something we hope to see more of in the future.

45 thoughts on “Homebrew 68k Extravaganza

      1. Freescale are still making 68000s. They’re marked as “Not Recommended for New Design”, but there’s so many of them in old embedded devices I don’t think they’ll ever be able to completely retire them. Low volumes do make them kind of expensive though.

  1. I’m pretty sure I’ve seen a homebrewed 486 based machine floating about on the Web, but my Google-fu is weak today. IIRC it was built on perf board with point to point wiring and had four EPROMS for bootstrapping it (as the bus width is fixed at 32-bit on the i80486).

  2. Sun and SGI did not yet exist in 1979.

    The 68000 was used in the earliest Unix workstations, such as the MIT Nu machine (which later gave the Apple NuBus its name). I was lucky enough to have a well used hand-me-down “old Nu” as my personal workstation in 1983. It had a vertical format bit-mapped screen with mouse-based GUI that would only seem slightly old-fashioned today.

    One notable aspect of 68000 based machines was they used a pair of 68000 processors. There was a bug (more of a “thinko”) in the page fault interrupt hardware. As a work-around, the second 68000 actually handled the page fault and fixed things up so that the primary CPU could continue.

    1. I used to write 68k assembler stuff, and I never came across the term ‘page fault’. I assume that term comes from processors which use segmented addressing like the x86, so do you mean something like a bus error or something else?

      1. A page fault is essentially accessing virtual memory that is not backed up by physical memory.

        The 68000 didn’t support virtual memory, but you could build a system using an external MMU. IIRC the problem was that when a page fault occurred, the faulting instruction could not be restarted. The solution was to use two processors in parallel, one running slightly ahead of the other.

  3. The well equipped 68008 in the youtube video is clearly a commercial product. The manufacturer logo is clealy visible as a silk screened Kiwi bird. Anyone able to identify the company from that ?

    Perhaps it came in kit form, or a bare PCB like the 68000 from the (amazing) German computer magazine C’T that I put together in 1985. I wish I had pictures of it.. All TTL, no PALs or custom chips. It was fun to play with and to build expansion cards for.

  4. FTR:

    The 68000 was used in a whole lot of pinball machines back in the 80s and even in the 90s on the late WPC machines from Williams a 6809 was in place.

    The new Stern machines changed to Atmel IIRC, but is was used over a really long era

  5. I loved the 68K, a great cpu with lots of registers and wonderful assembly language. No Intel alternative was even remotely comparable both in power and ease of programming, but Intel eventually won just because they came first in the personal computer world.

    1. By modern standards a 68000 is very slow, and as a microprocessor it doesn’t have all the built-in peripherals you might expect.

      Microcontrollers are designed to run code from internal memory. Some can run code from external memory, but usually at a cost – either in speed or by imposing restrictions on usage (eg. no simultaneous CPU and DMA access). So there are MCUs you could use for a general-purpose computer, but you have to be careful when picking one.

  6. Even if Freescale has retired the architecture, one can go to Opencores.org and use one of the fully-verified VHDL re-implementations available there if one wants to make a hardware system based around the 68k.

  7. > I lamented the lack of builds using the
    > venerable Motorola 68k.

    You need to work a bit harder on your research then… There are tons of people doing stuff with real 68000s (The 68sec000 is very nice for FPGA projects) and with TG68. I’m still looking for someone that has some real 68040V chips..

      1. Yep,

        They are crazy expensive. The 68sec000 and 68040V are the only 3.3v chips in the series though (the 68060 is 3.3v core but 5v IO from what I gather).
        I think freescale have actually stopped production of all of the real 68000 series expect for maybe the 68sec000.. and even those are hard to get in small quantities. I had a quote from a Chinese dealer for $25 for the 68040FE25V .. considering how hard it is to get less rare real 68060s from China I’m not sure if will bother testing the water..

      2. I don’t think they’ve stopped producing them altogether, because in the parametrics they have a separate “No Longer Manufactured” category. However I’d guess they only crank a wafer through production when a large customer comes looking for spare parts.

        Any parts bought from China would almost certainly be recovered from scrap or fakes. The 68040/060s heydays predate the rise of Chinese electronics manufacturing, so there’s just no reason for lots of these chips to be sitting around in the region.

  8. For real old-school homebrewing of the 68000, you have to read the original, early 80′s “DTACK Grounded” newsletters, written by one of the first hobbyists to try to use in a simple system, not a heavy Unix or fancy GUI box. Heavy with the hardware and software details. Be prepared to set some time aside! All written by one engineer with very strong opinions, right in the middle of the 80′s PC craze.


  9. No mentions of the derivative 68HC series of micro-controllers?!? My entry into hacking micros was with their F1, which fully exposed the address and data busses. I burned their \”buffalo\” boot loader onto a 27c16 eprom using a GR-2272 in circuit tester. Those were the days.

  10. many years ago in a different life, I designed a 68030 based computer with a open design. the board had a ISA bus and a boot prom that could use IDE drives and a VGA controller. it has a dram controller that could talk to 4Mb of SIMMs. at one time a protected mode Minix was ported to it. it worked well enough to be able to compile itself.

    the design files and source code for the bootprom live on in the net…


    a series of articles were published in circuit cellar.

    I might have some pictures and even have one of the wirewrap prototypes and maybe one of the final PCBs.

    1. This step down memory lane is fun.

      Is there any open source compilers for the 68K ?

      Are there any open source compilers for the 683xx ?

      Debugger and BDM interface would be nice as well.

  11. In the 80’s Peripheral Technology in Atlanta sold the PT-68K, which was a single-board computer designed by Peter Stark. It had the great advantage that it fit in a standard PC-AT enclosure, worked with the PC display and keyboard, and looked exactly like a PC. This let you build a system using the very cheap PC components. It ran at 20MHz and had, as I recall, 2MB of RAM.

    PT later came out with 68020 and 68030 versions.

  12. The nicest part of the 68000 was that it was a static chip as opposed to a dynamic one. This meant that you could run it at any frequency from DC on up. Use a pushbutton as a toggle, if that suits you. It also needs next to nothing in terms of support chips. You don’t even need a clock chip. Just hang a crystal right across the clock pins. Or even an R-C time constant.

    Add a couple of ROM and static RAM chips, and you’ve got yourself a computer.

    Peter Stark’s design let you build the system a piece at a time. For the 68000, the hex instruction 0000 is NOP, so if you tie all the data lines low, it will free-run and you can watch the address lines count up.

    Let me repeat that. Put a 68000 on a board, add a crystal, and power,and you’ve got a computer that runs. Stark next build the chip select circuits, and you could tell they were working by looking at the output waveforms.

    Actually, you didn’t even need a scope. He borrowed the LED from the HD circuit to use as a poor man’s logic probe.

    I had gotten as far as learning these neat features of the chip, and made the career decision to build a system from scratch, when I read Peter’s article and realized he’d already done it.

    Ditto on those who said the 68332 has all the makings of a system-on-a-chip. Doesn’t have ROM, RAM, or analog I/O on chip, like modern microcomputers do, but those are easy to add, these days,

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