[GreenKeys] Parallel to Current Loop Conversion

[Jim Haynes]

On Thu, 4 Dec 2014, Cory Heisterkamp wrote:

> Before I go and reinvent the wheel, I was wondering if anyone had a proven
> old school circuit (no micros) for converting parallel 8-bit data to
> ASR-33/35 friendly 110 baud equivalent. This won't be a computer interface,
> rather the parallel source will either be switches or relays with an
> additional line to 'release' the data when ready.
> 
If it's a Model 33 that's involved, note that the keyboard and tape reader
contacts are open when they are not transmitting, so you can connect your
relay-contact parallel signal to the M33 distributor and then kick it
off when you are ready to send a character.  This is the way it was done
in the console terminal for the Burroughs B5500 computer, if I remember
correctly.