One more try - Can you ID this S-100 Serial board?

Chris Elmquist chrise at
Thu Oct 1 20:26:25 CDT 2015

On Thursday (10/01/2015 at 07:30PM -0500), drlegendre . wrote:
> @Chris / All
> Unfortunately, I've never eyeballed the logo of the locally-based MCT corp
> so I can't comment on it, but again, it's an intriguing thought. And yes,
> it's quite possible that the PO knew or ever purchased this Altair from an
> employee there. He (PO) indicated that he bought the system second-hand, in
> the early 1980s, from an engineering colleague who worked elsewhere in the
> locality.

So, I'm still betting lingonberries to lefse that the PO that the PO
got the machine from might have worked at MCT and possibly even designed
said board and so knew how to use it in an Altair while it was normally
used in a more dedicated, purpose built system.

I know for a fact that the local power company (called NSP in the day)
was doing a lot of work with S-100 systems for monitoring and control
applications in '78 and '79.   So, the word was out and a lot of these
outfits were seeing the commercial upside to "personal computers" in
the late 70s around here.  S-100 machines were easy to get by then.

> And the PO is the kind of guy who would have hacked-out the cheapest and
> most expedient solution to whatever was presented. Don't get me wrong, the
> guy is quite sharp and well-educated, but just a real practical 'bailing
> wire and duct tape' kinda guy.. half EE, half farmer or something. ;-)

And so his fishing buddy gave him a board that "fell out" of the lab at
work and he promptly put that baby into service in his Altair.

There were a lot of S-100 machines built around here, with 16K or 32K
of 2102 SRAMs, all of which came out of the QA department at CDC as
an example.

Of course I am offering all of this as theory but having lived these
exact experiences, I feel like it's the truth :-)

> Oh - about it being a 'kit'.. I gave a good look, and it's hard to say for
> sure, but the board +is+ totally hand-soldered. But the work is excellent.
> So it's either a well-built kit or a smaller-run factory board - but it
> wasn't wave / batch soldered.

I know that Multi-Tech made and shipped tens of thousands of modems
throughout the 70s and 80s that were all hand soldered by some nice
ladies that worked in a very large room at the back of the company in
New Brighton, MN.  I don't think you start to see a lot of flow or wave
soldering for products made around here until the mid to late 80s.

> Also, I'm curious about the 50-pin headers.. why were they never installed?
> All of the other work was done, all the expensive parts (chips) are
> in-place - so why not a couple of cheap headers? Yes, a few resistor SIPs
> are gone, as is one chip missing, but still, you get the point.

Good chance those connectors were the most expensive part on the board
then.  Might have also been a build option depending on how the board
was used and this one was nabbed from a situation where those interfaces
weren't used.


> On Thu, Oct 1, 2015 at 6:56 PM, Chris Elmquist <chrise at> wrote:
> > On Thursday (10/01/2015 at 06:27PM -0500), drlegendre . wrote:
> > > Now a question..
> > >
> > > Can someone give me a quick rundown on how the CPU communicates with this
> > > board? Does the board show up as a few bytes in the memory map, like on
> > > page zero? Does it connect directly to some registers in the CPU? How
> > does
> > > data move from the CPU / buss into & out of the board?
> > >
> > > In short, how does the computer know where to "find" the board - and how
> > do
> > > they converse? I'm only concerend with the serial portion, the rest is
> > > still a mystery - the 50 pin headers might be anything from parallel
> > ports
> > > to (proprietary?) controller interfaces.
> >
> > This is where I'm holding onto my theory that it is a custom design for
> > a specific purpose--  as I do not see the usual jumpers or DIP switches
> > to set I/O or memory addresses.    If it were a generic card built for
> > general purpose use, it would almost certainly have DIP switches to set
> > an I/O or memory address decode.
> >
> > On S-100 systems, you have both I/O and MEMORY space.  Things like serial
> > port cards were almost always in I/O space and were decoded within a 256
> > byte block.   Different S-100 systems had their console or other I/O at
> > different addresses and with different chips (8251, 6850, 2661 and other
> > UARTs with internal register sets as well as TR1602, AY-3-1015 and similar
> > "dumb" parts).
> >
> > Without any jumpers or switches to set the decode, you will have to
> > reverse the design to figure out how they did it.  It might be I/O
> > mapped but it might be memory mapped since it was likely purpose built
> > for a specific application.  Along with this, you will probably not have
> > operating system support that understands how to talk to this setup so
> > you will need to modify a CP/M BIOS or other OS I/O support to understand
> > how to talk to it.
> >
> > The AY-3-1015 UARTs are "dumb".  Their framing format is decided by
> > strapping inputs to the chip and then they present a byte-wide input
> > register and output register and strobes to read or write those registers.
> > This would likely be handled by buffers with enables to gate these paths
> > onto the S-100 bus.
> >
> > I concur with Chuck that there were and are a lot of "MCT" companies.
> > I just have a high confidence that the logo on Bill's board matches the
> > logos I am familiar with for the local MCT here in town.
> >
> > Chris
> > --
> > Chris Elmquist
> >

Chris Elmquist

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