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

Rod Smallwood rodsmallwood52 at
Thu Oct 1 07:54:16 CDT 2015

I have been doing a bit of spadework on this one.
There was a company call MCT who advertised in the PC Mag.  in the early 
The products were add-ons for PC's.
The possibiliy that they made S100 products prior to 1980 is not an 
unreasonable one.
So anybody with an early 80's PC Mag might find them. In fact any 
publication from about
then may have a reference.


On 01/10/2015 13:30, tony duell wrote:
>>> I'm fairly certain this is a serial board - mostly because the PO told
>>> me so, and when I received it, it had a 25-pin male connector on a
>>> three-wire cable carelessly soldered to the pads behind one of the
>>> cable headers on the top edge. But the cable was removed as a matter
>>> of course when I was prepping the machine for a rebuild. I mistakenly
>>> assumed that the docs would be trivial to locate - so no need to
>>> record the original wiring connections.
>> no disputing that.  Glad Tony made his point, I was curious if it was
>> early enough to not have had what we are accustomed to now days.
> Does 'now days' include RS232 interfaces :-)
> But before the 1488 (or at least before it was common), many manufacturers
> used op-amps as RS232 drivers. Look at the HP11205 and 11206 interfaces
> for the HP9830, for example.
> For input I could believe taking the signal through a resistor to a zener diode
> to ground. Remember a zener is reverse-biased in 'breakdown' mode so
> that circuit will clamp +ve voltages to the zener voltages and -ve voltages (where
> the zener is not the normal way round and therefore acts as a normal silicon
> diode) to -0.6V. Or indeed resistor +diode clamps to +5V and ground. Then into
> a TTL gate.
> Given that the original connection was 3 wires, it's a good bet they were TxD, RxD and
> ground. Ground should be trivial to find. The trace the SO output of the UART to an
> op-amp and then to the header. Similarly trace SI back through a TTL gate (which has
> been mentioned already) to a header pin. I can't believe this is a complicated circuit....
> OK, I've been doing this sort of thing for years, but I wouldn't be surprised if
> I could trace those connections in less time that it's taken to try to look for the
> docs...
> -tony

Wanted : KDJ11-E M8981 KK8-E M8300 KK8-E M8310 KK8-E M8320 KK8-E M8330

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