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

drlegendre . drlegendre at
Thu Oct 1 20:54:16 CDT 2015

Here's more grist for the mill. I did contact and receive a reply from
gentleman Herb Johnson at retrocomputing. I hope he doesn't mind if I quote
his comments here.. they seem quite pertinent and they reflect or
complement many of our working assumptions.

Herb Sez:

"Warning: I'm offering advice, which I do not warrant in any way. I am not
responsible for loss, injury or damage to you or your equipment or
software. Use any information, advice or suggestions I make, entirely at
your own risk. Always work with caution.

1) identify big chips. AY-3-1015 is a UART, so is AY-3-1014. The crystal is
probably a baud rate generator. Those two small connectors near the UART
are probably serial ports. If you trace the lines and chips near those
connectors, you can decide what some of the lines are. the UARTs have
transmit and recieve pins so you can trace through from there.

My guess is that the serial connectors are NOT "RS-232" because of all the
resistors and caps.

2) identify connectors. There's two 50-pin connectors but they are not
"populated". I see 74LS373 and '374 chips, those are 8-bit I/O devices. You
can trace those, probably, to those connectors. This suggests the
connectors are "parallel ports".

3) look at the S-100 connector. there's not that many S-100 pins wired to
the board. That suggests it's an I/O board, which often only uses the lower
8-bits of address (and of course both 8-bit data line sets).

4) follow the traces. So it's likely this is a serial/parallel I/O card. If
you follow a few address lines from the S-100, you'll find where they are
decoded to specific I/O addresses, and see probably some jumpers to change
that address.

5) tests. Before plugging the board into the bus, check the DC power lines
for shorts. Check with an ohmmeter across all "tantalum" capacitors for
shorts (under 100 ohms about) and replace those caps. When you apply power,
confirm the regulator produces 5.0V. Be prepared to shut down your S-100
bus power at ANY sign of heat or smoke - and identify immediately any
burned component. I often use a Variac to control power to a S-100 card or


I recognize "MCT" as a brand of S-100 boards, but I've not owned docs for
them, I don't believe. When you see MCT branded cards discussed, you might
ask owners about documentation. I should create a list of undocumented
S-100 cards, just for these kinds of boards.

Let me know if any of the above information is helpful and any results from
checking out your card as suggested. OK? Good hunting!"

Thanks again, Herb - your time is sincerely appreciated! Nice to know a guy
like that still has time for a newbish enterprise as this.. ;-)

On Thu, Oct 1, 2015 at 8:26 PM, Chris Elmquist <chrise at> wrote:

> 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.
> Chris
> > 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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