[GreenKeys] Got Model 33 working from PDP-8
Eric Moore
mooreericnyc at gmail.com
Sat Oct 11 21:19:35 EDT 2025
Wonderful and congrats!
FYI, your message was a bit garbled.
-Eric
On Sat, Oct 11, 2025, 8:09 PM Jones, Douglas W via GreenKeys <
greenkeys at mailman.qth.net> wrote:
> <div class="elementToProof">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:</div><div
> class="elementToProof" style="font-family: Aptos, Aptos_EmbeddedFont,
> Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 12pt;
> color: rgb(0, 0, 0);"><br></div><div class="elementToProof"
> style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService,
> Calibri, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0,
> 0);">06000 7200
> CLA
> / AC = 0</div><div class="elementToProof" style="font-family: Aptos,
> Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif;
> font-size: 12pt; color: rgb(0, 0, 0);">06001 6046 A,
> TLS / main loop top, send
> AC to TTY</div><div class="elementToProof" style="font-family: Aptos,
> Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif;
> font-size: 12pt; color: rgb(0, 0, 0);">06002 6041 B,
> TSF /
> polling loop top, skip if TTY done</div><div
> class="elementToProof" style="font-family: Aptos, Aptos_EmbeddedFont,
> Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 12pt;
> color: rgb(0, 0, 0);">06003 5202 JMP
> B / polling
> loop
> bottom</div><div class="elementToProof" style="font-family: Aptos,
> Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif;
> font-size: 12pt; color: rgb(0, 0, 0);">06004 7001
> IAC /
> advance to next character</div><div class="elementToProof"
> style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService,
> Calibri, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0,
> 0);">06005 5201 JMP A
> / main loop bottom.</div><div
> class="elementToProof"><br></div><div class="elementToProof">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 ha
> s 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.</div><div
> class="elementToProof"><br></div><div class="elementToProof">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.</div><div class="elementToProof"><br></div><div
> class="elementToProof">Work remaining? Lots:</div><div
> class="elementToProof">-- TTY input</div><div class="elementToProof">--
> Tally High-speed paper-tape reader input</div><div
> class="elementToProof">-- BRPE punch output</div><div
> class="elementToProof">-- Point-plot oscilloscope display output</div><div
> class="elementToProof">-- Analog-to-digital multiplexer and converter
> input</div><div class="elementToProof"><br></div><div
> class="elementToProof">If we can get that much working, we'll b
> e able to build some joysticks (using 1965 technology, of course) and run
> some really nice games from that era.</div><div
> class="elementToProof"><br></div><div class="elementToProof">
> Doug Jones</div>
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