68k homebuilts

[John Floren]

On Fri, Dec 12, 2008 at 4:06 PM, Tony Duell <ard at p850ug1.demon.co.uk> wrote:
>>
>> Hi everyone
>>
>> As a 4th year computer engineering student with a part time job, I
>> definitely have too much time on my hands, so I've been thinking about
>> doing something like building my own computer. I remember playing with
>> the 68k SBCs back in my assembly class, so I thought something from
>> that family might be an interesting choice. It's ambitious, but
>> ideally I'd like to do 16/32 bits and a few megs of memory.
>>
>> Have any of you built something like this? I'm looking for links to
>
> I've built several machines from scratch, but never a 68K-based one. But
> I do feel that's a pretty good choice for a processor :-)
>
> I would start by tracking down a _second edition_ of the 'Student Manual
> for the Art of Electronics' (that may not be the exact title, but if you
> can't find it I'll dig out my copy and post more details). This is the
> 'laboaratory book' for the famous 'Art of Electronics' book (which you
> should have anyway :-)), and the last few exercises are making a
> 68008-based computer (so 8-bit data bus) with something like 8K of static
> RAM a bit of I/O, etc. You won;t want to copy that design, but it'll give
> you ideas.
>
> As regards RAM, I really would use static RAM, at least to start with.
> It's a lot easier to work with than dynamic RAM, and SRAM is getting
> pretty cheap these days.
>
> You also need to think what I/O you want. Do you want a toggle-switch
> panel to load ROM, a monitor program (hex keypad and display, or an ASCII
> terminal interface?), a bootstrap for some larger OS (to be loadrd from
> what device?) and so on. Personally, I'd probably add a serial port and
> have a simple machine code monitor in EPROM, but it's up to you.
>
> -tony

Well, part of my motivation for doing this is that I'm really an
operating systems guy, so in a perfect world I'd be able to make
something I could hack around with easily. With that in mind, I'm
thinking a serial terminal interface, but also including a front panel
with toggles and lights to play with. It would be really fun to go so
crazy as to do a PDP-11 to the point where I could boot one of the old
OS's, but that may be too ambitious for me at this time (can you even
buy PDP-11 microprocessors anymore?).

Given my druthers, I'd go with a 32-bit system, but I'm not sure if
that will increase the complexity beyond my abilities. I'm competent
with soldering and ok when it comes to breadboarding; things could
quickly go downhill if I tried to assemble on perfboard since I've
only tried that for very small circuits. The whole process of
assembling a computer system from the chip level is new to me, so any
tips would be appreciated. My reasons for preferring 32-bit is that
the potential capabilities are much greater.

What does it take to do video (bitmapped) output, by the way? That
would be especially interesting, in my opinion.


John
-- 
Ph'nglui mglw'nafh Cthulhu R'lyeh wgah'nagl fhtagn