On Apr 9, 2021, at 10:22 AM, Rob Gowin <robg@fastmail.com> wrote:

[I see that Dan C. has already covered some of this.]

On Fri, Apr 9, 2021, at 6:13 AM, U'll Be King of the Stars wrote:

I've never seen a 68k SBC.  Have I missed out something along the way? 

Is there a community for 68k SBC's?

There is a community of folks making 'retro-brew' computers, which are new home-brew board designs based around older CPUs. While Z80/Z180 based designs are the most popular, there are a smattering of 68K retro-brews. The main places for discussions are https://groups.google.com/g/retro-comp and https://www.retrobrewcomputers.org/forum/index.php. The availability of very cheap PCBs from China (2 layers, 10cm x 10cm, $3 per board shipped, shipped in a week) and open source PCB design software like KiCad seems to have increase the amount of this kind of activity over the past few years. 

Hardware-wise, most of these are 68000's with some ROM (around 512K is typical), some SRAM (512K to 1 MB), a UART of some kind, and perhaps some storage either SDCard via SPI or CompactFlash via an IDE port. I think only the Kiwi68K supports any type of video, using a vintage TI video chip.

Here are a few links to 68K designs:

ECB Mini-68K CPU Card (68008 based and not a single board) - https://www.retrobrewcomputers.org/doku.php?id=boards:ecb:mini-68k:start

ECB KISS-68030: (68030 based and not a single board) - https://www.retrobrewcomputers.org/doku.php?id=boards:ecb:kiss-68030:start

The Rosco M68K: https://rosco-m68k.com

The Tobster 030 - https://www.retrobrewcomputers.org/doku.php?id=builderpages:tobster:t030

Jeff Tranter's 68000 - http://jefftranter.blogspot.com/2017/01/building-68000-single-board-computer_14.html

Plasmo's Tiny68K - https://www.retrobrewcomputers.org/doku.php?id=boards:sbc:tiny68k:tiny68k_rev2

Plasmo's CB030 - https://www.retrobrewcomputers.org/doku.php?id=builderpages:plasmo:cb030

Kiwi68K - https://www.ist-schlau.de

All these designs are open source. The Rosco one is available as a kit on Tindie.com. (I have no affiliation.) I've got my own 68008 based board that I'm working on, but haven't published anything about it.

--

I think the main reason the 68K is not more popular in the retro-brew/DIY community is lack of software. On the Z80 side, once you've built a board there is a ton of CP/M-80 software available to run. For 68K boards, the usual software progression is a ROM monitor, then maybe porting of Lee Davison's EhBASIC, then CP/M-68K. CP/M-68K has very little software available, and what is available are microEmacs and a few compilers (K&R C, BASIC and Pascal). That's about it for 68Ks without an MMU. A couple of the boards above that have 68030 do have Linux running on them. There's also the perception that Z80s have an easier hardware interface, but I'm not convinced that's true. 

-- Rob 

ECB Mini-68k CPU Card

I should disclaim that some of the things I'm about to link to are kits sold on Tindie.com. I have no affiliation with the creators, other than being a fan of their work.