[sdiy] OT: COSMAC Elf 2000

[Roy J. Tellason]

On Saturday 02 February 2008 02:01, Phillip L. Harbison wrote:
> Roy J. Tellason wrote:
> > anthony wrote:
> > > At first I read the project article avidly, hoping
> > > for  a cool project that might consume a lion's share
> > > of my vast TTL logic collection.
> >
> > Dunno why. [...] It ain't TTL.
>
> Indeed, it is 4000-series CMOS which is not particularly fast even by 1976
> standards. Are 4000 series parts even available now? I thought they were
> replaced by the 74HC and 74HCT series.

They are in new designs,  and I read recently that those 4000-series parts 
were "in decline",  and I know of one manufacturer that's switching away from 
them or already has.  But they'll also handle 15V logic levels just fine,  
which is something that none of the newer series parts will do AFAIK.

> > > [...] I could probably make an Altair clone
> >
> > Somebody's already doing that,  with a web site and everything,  though I
> > don't have a URL handy at the moment.
>
> You may be thinking of Briel Computers, but their Altair clone is a clone in
> appearance only. Inside lurks an ATX motherboard with a Pentium 4. The only
> resemblance is the front panel and I'm not sure it is functional. While the
> switches and lights are impressive on an Altair (and even more impressive on
> an IMSAI), I would not want to go back to the days of using them for real
> work. 

I may be,  but I'm not sure.  It's been a while since I ran across that.

> > > I have all sorts of 74LS373's and 74LS374's and a few
> > > 8088's. I know that the original Altair was based on
> > > an 8086, but the switch shouldn't be too hard.
> >
> > Nope.  The original Altair 8800 was based on the 8080,
> > which is a whole different thing entirely. [...]
>
> While you're technically correct, note that he said he
> had an 8088 which is the 8-bit version of the 8086.

Still a whole different chip though.  :-)

And I don't like 'em much.  Segment registers?  Ugh!

> That might not be too difficult to adapt to the S-100 bus.

It's been done,  I think.  Godbout,  and maybe some others sold 'em. That bus 
also supported the 68000 (Cromemco) and probably a bunch of other chips 
besides.

> I think the control signals (/RD, /WR, etc.) are mostly common across both
> chips. The original S-100 had only 16 address lines whereas the 8088 has 20;
> however, he could either put a megabyte on the CPU board or use the
> IEEE-696 spec (which added 8 additional address lines). 

Yup.  It's also speed-limited.  In my case I have a board w/ Z80 CPU and ROM 
monitor and some I/O on it,  and a separate board for the RAM,  which I'm not 
that happy about.  My Cromemco System/3 also has that same sort of division, 
and for some reason they chose to use a bunch of bus lines as bank select 
rather than address bits.  If I were building anything for either box I'd put 
the RAM and CPU on the same board,  as much RAM as I could fit,  and let the 
I/O sit somewhere else if I had to...

> I guess the remaining question would be... why bother?

Well,  for an 8088 I wouldn't.  But that's me.  I do think that the early 
systems are fun once in a while but wouldn't try to use them to do any kind 
of serious work these days.

> > Hey, blinkenlights are cool.  But I haven't figured out anything that
> > justifies using a bunch of them yet,  nor the 7-segment displays I have
> > either. 
>
> Neither have I, and this is coming from a guy who has spent many a man-month
> using Altair/Imsai/KIM/AIM front panel switches to enter hexadecimal code,
> or entering hand-assembled code into an EPROM programmer. I do not
> relish the idea a returning to those days.

Nope!

> If your main goal is to design and build *synthesizer* hardware, I do not
> see any reason to return to such primitive tools no matter how big your pile
> of 1970's era computer parts may be.

Neither do I.  Though my interests aren't necessarily limited to synth-type 
stuff.

> Actually, I am working on a design that will use 2048 LEDs, but not for a
> traditional front panel. It will have one status LED per processor.
>
> With that said, I return to lurk mode. :-)

You're working on something that has 2048 processors?  Hm...  :-)

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