[GreenKeys] Got Model 33 working from PDP-8

[Jones, Douglas W]

<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.&nbsp; 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.&nbsp; We have yet to get the TTY keyboard input data path to work, but I'm betting we are only days away from that.&nbsp; 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 &nbsp; &nbsp; &nbsp; &nbsp; CLA &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; / 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, &nbsp; &nbsp; &nbsp;TLS &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; / 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, &nbsp; &nbsp; &nbsp;TSF &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; /&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;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 &nbsp; &nbsp; &nbsp; &nbsp; JMP &nbsp; &nbsp; B &nbsp; &nbsp; &nbsp; /&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;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 &nbsp; &nbsp; &nbsp; &nbsp; IAC &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; /&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;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 &nbsp; &nbsp; &nbsp; &nbsp; JMP &nbsp; &nbsp; A &nbsp; &nbsp; &nbsp; / 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.&nbsp; 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.&nbsp; 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?&nbsp; 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 be 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">&nbsp; &nbsp; &nbsp; Doug Jones</div>