[GreenKeys] Got Model 33 working from PDP-8

[John Doe]

For those who wanted to read the original message un-garbled, I've re-typed
it below - hopefully without error:

Thursday afternoon, a student and I finally got the U of Iowa's
PDP-8 (s/n 85) to send output to our Teletype Model 33. It's
taken about a decade of work with students to get this far,
including a near ground-up rebuild of the Teletype, reforming
the PDP-8 power supply capacitors, tuning the memory
(incompletely, at this point), and replacing a large number of
silicon switching diodes (plus a few transistors) in the PDP-8.
We have yet to get the TTY keyboard input data path to work,
but I'm betting we are only days away from that. Here's the
program that we used, successfully:

06001 6046 A, TLS  main loop top, send AC to TTY
06002 6041 B, TSF  polling loop top, skip if TTY done
06003 5202 JMP B   polling loop bottom
06004 7001 IAC      advance to next character
06005 5201 JMP A   main loop bottom

Not very exciting, just repeats sending all 256 8-bit values to
the TTY over and over (and since the TTY ignores the top bit,
each run of 256 values is 2 runs of the 128 ASCII codes,
including CR, LF and BEL in each run, so we get lots of lines
of output. Since the Model 33 folds upper and lower case, each
line has 2 repeats of the upper-case alphabet, but piles up
lots of characters on the right edge of the page because the
lines are over-long. Still, a great step in our hardware
restoration effort.

The machine was delivered to the U of Iowa in November or more
likely December of 1965, so we have enough working to do some
nice demonstrations for the machine's birthday.

Work remaining? Lots:
-- TTY input
-- Tally High-speed paper-tape reader input
-- BRPE punch output
-- Point-plot oscilloscope display output
-- Analog-to-digital multiplexer and converter input

If we can get that much working, we'll be able to build some
joysticks (using 1965 technology, of course) and run some
really nice games from that era.

Doug Jones
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