[HN Gopher] Minimal single-board computer based on Motorola 68000
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Minimal single-board computer based on Motorola 68000
Author : homarp
Score : 67 points
Date : 2020-07-29 20:28 UTC (2 hours ago)
(HTM) web link (github.com)
(TXT) w3m dump (github.com)
| rvense wrote:
| Another new 68k board that came out recently is Rosco:
|
| https://rosco-m68k.com/
|
| It's for sale on Tindie and the person who made it seems to
| focusing a lot on making a toolchain available etc. If you want
| to actually programme the 68k it looks like a good bet.
| jjoonathan wrote:
| > Due to the minimal address decoding circuitry, accessing
| certain memory regions will cause multiple devices to be
| selected. This should be avoided.
|
| Two bus drivers enter, one bus driver leaves!
| mytailorisrich wrote:
| Great. At 12MHz and 1M RAM that's still above an Atari ST or
| Amiga 500.
|
| There used to be plenty of such computers based on 8bit to 16bit
| discrete CPUs (Z80, 680x, 8255, etc), with schematics in
| electronics magazines.
|
| This was great because everything was simple enough that you
| could fully understand and use 100% of the hardware yourself and
| code 100% of the software yourself. And all components were
| standard discrete ones (like this project), not SMCs, so there
| were also very easy to handle.
|
| You did not even need a PCB. I once built such simple computer
| based on a Z80 using good old wire wrap [1] on a prototyping
| board, which was quite a common thing to do, but quite a torture
| to be honest and I would not want to try with a 68000...
|
| [1] https://en.wikipedia.org/wiki/Wire_wrap
| jacquesm wrote:
| Having worked on a fairly large 68K board that was wire wrapped
| I would not recommend it.
| ChuckMcM wrote:
| Just needs a frame buffer and you almost have a Sun-1.
| yjftsjthsd-h wrote:
| Clarification on the "Forbidden (multiple devices selected) " bit
| - Am I reading correctly that the memory addressing is,
| essentially, a little buggy as a side effect of optimizing for
| simplicity, and that results in mapping multiple things to
| certain addresses?
|
| Also, I somehow didn't realize that you could buy what appears to
| be a new 68000, and for $8.95 (https://www.jameco.com/shop/Produc
| tDisplay?catalogId=10001&l...). In my defense, last time I
| searched it wasn't obvious, mostly because nobody labels it as a
| "68000"; it's a 68HC000P-12, which only in the details is listed
| as a "6800" (sic) family - I assume that's just a typo. And to be
| fair, I'm sure most people looking for a 68000-series know how to
| look for it; it's like expecting people to know that a 80486 is
| an x86 usually called a 486. Just a bit of friction for a newbie.
| Animats wrote:
| The 68010 is sort of a "fixed" 68000. Restoring state after a
| page fault doesn't work right in the 68000.
|
| If it had, 68000 machines with MMUs would have worked right,
| and the history of computing might have been more Motorola and
| less Intel. (The Lisa and the Apollo Domain did have 68000s
| with MMUs and horrible kludges to make them work.)
| jacquesm wrote:
| This was quite common. You only decode out as much as you need
| and if that results in phantom appearances of devices or ROM as
| long as it doesn't interfere with the operation of the device
| that is perfectly ok. Memory map aesthetics are important but
| sometimes circuit simplicity is more important.
| Taniwha wrote:
| I think it's still 'buggy' if the result is a bus fight (that
| might actually damage chips)
| yjftsjthsd-h wrote:
| That's fair; I hesitated to call it buggy, because a well-
| understood bug that's documented and easy to work around or
| ignore and which nets you some benefit is only barely a bug
| at all.
| mng2 wrote:
| I'd classify it under "hack that is fine if you know what
| you're doing". Fancier 68K systems would use a PAL for
| address decoding, primitive programmable logic.
| jacquesm wrote:
| If you want the same instruction set and and even smaller board
| you could use the 68008:
| https://en.wikipedia.org/wiki/Motorola_68008 they're going to be
| hard to find though.
| mark-r wrote:
| I wonder why they used a 68000? The 68020 was a significant
| upgrade, and other than not being a DIP package it made a great
| SBC.
| tyingq wrote:
| He did mention through hole being desirable. A DIP 16Mhz 68010
| could be an easy upgrade. And you would get virtual memory
| addressing.
| icedchai wrote:
| 68010's still need an MMU for virtual memory. So do 68020's,
| now that I think of it.
| tyingq wrote:
| I see some evidence that an MMU is optional:
| https://news.ycombinator.com/item?id=7684824
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