[GreenKeys] Parallel to Current Loop Conversion

[Cory Heisterkamp]

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.

Intersil use to make an IC that would generate various bit rates including
110, and I could sequence a pair of 8-bit shift registers (8 data plus a
fixed start and two stop bits) to drive a relay for the current loop. A
4-bit counter would reset the shifters. With a couple dip switches I could
reconfigure this for 5-level Baudot at a different bit rate to play nice
with the model 28's.

Or maybe I should hack an old test set. Thoughts?  -Cory
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