MCT Serial board mystery - Can you crack the pinout code?

Chuck Guzis cclist at
Sat Nov 15 15:02:42 CST 2014

On 11/15/2014 11:52 AM, drlegendre . wrote:
> Oh, and to add to my confusion.. I've read that the early Altair serial
> boards used a 20mA  current-loop transmission standard.. which as far as I
> know, is +not+ standard RS-232 stuff. So should I actually expect this
> board to be a standard RS-232 device, or is it something else.?

I have an Altair SIO-1 board.  Yes, it can drive a TTY, but that's just 
an option.  I used it in RS232C mode.  One serial port on an S100 
board--waste of space.

If memory serves, the only terminal MITS originally sold for the Altair 
was an ASR-33 TTY, so the current-loop interface was important.


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