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Pdp 8 or early 11 wiring to asr 33 question

billdeg

billdeg

Technician
Joined
Nov 17, 2003
Messages
3,885
Location
Landenberg, PA USA
Can someone confirm something for me? Here is a scan of the wiring coming from the pdp 11/05 console card, which I believe would be the same as the pdp 8 or 11/10 11/20.

http://www.vintagecomputer.net/teletype/asr33/M9970_TTY.pdf

If you look at table 3.5 can someone tell me if I have terminal strip posts you connect to coming from the mate and lock connector holes 2,3,5 and 7 correctly wired?

I have them set
Transmitted data return (-) pin 2 attaches to terminal strip screw 6
Received data return (-) Pin 3 attaches to terminal strip screw 3
Transmitted data send (+) pin 5 : Terminal Strip 7
received data send (+) pin 7 : Term strip 4

I can send from the computer but cannot receive from asr 33. The asr 33 works fine for other computers. I am detecting the key pulses coming from the teletype. I have loaded the standard echo chars program but I cannot echo characters back though the computer back to the asr 33 printer. I have an 8k in core.

If the wiring is correct then I have to focus on the computer but I just want to be sure I have the teletype wired correctly, I have never actually confirmed for sure with an actual pdp connected to a teletype that I have it connected correctly.
 
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Found this:
http://www.pdp8online.com/pdp8cgi/query_docs/tifftopdf.pl/CHD/LT33_print_set.pdf

which I believe means that I have it right. See page 2.

Apparently there are changes you need to make to a stock ASR 33 in order to communicate with a DEC computer. Being that I have a stock wiring unit, I will have to settle for receive only mode until I can get the rest of the wiring and install a "reader run" circuit. DEC sold a reader run circuit board, part number 4915.

Bill
 
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Man that’s hard core running an ASR teletype with the PDP, old school all the way! Going to use paper tape to load programs from the ASR?
 
Yes all papertape. I want to build a system that relies solely on the ASR 33 for I/O, printing, and program storage. My goal is to make an ASCII art development system.

B
 
It seems to me my asr33 used a current-loop connection to my pdp-8/e. I don't have any info on the wiring though, and I don't know if the serial interface would be the same in an 11/05.

If you have rs-232 instead, the standard 3-wire wiring that works with pretty much any rs232 device with a db-25 connector is to have pins 2->3 ; 3->2 and 7->7 run between units, and at each end jumper 4->5 and 6->8->20, and enable x-on/x-off flow control in both devices.

Dunno if any of this is useful, but maybe this is: Happy new year!
 
Thanks doug but I am working to complete the DEC TTY mods and use the device for storage and all i/o, without rs232. It would be so much easier to just add a m7865 serial card to the mix and hook up to a laptop to download simulated paper tapes at a higher baud rate, I agree.
 
Fixed the problem, I can now send and receive from the teletype. Long story "short" I had two cables attached to the teletype for convenience purposes. One for the SWTPc using the UCC-6 connector #2, and one directly attached to the terminal strip for general use. The problem is, the SWTPc cable uses a common I/O connection (transmit and send), effectively shorting out the send from the teletype as far as the PDP 11 is involved. Removed the cable from connector #2 and now the pdp 11/05 can both send and receive. I mistakenly thought that if the cable on connector #2 was not attached (to a computer on the other end) it would not interfere with something attached directly to the terminal strip. Forgot about the common I/O jumper on the other end of the cable.
thm_wires_to_TTY_pic5.jpg

Note how the black and red wires are soldered together at pin 7

Before all this I worked with Malcolm (Mal on this forum) to check out my M7260 boards, but the baud rates were adjustable to tune them, but we were getting confusing voltages due to the cable problem.
 
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Looking good!

Been a long time coming there buddy. Your persistence is remarkable.
 
Checked out the video over on you tube and have to say it again, you the man! Very impressive. How many tapes are required to load Basic onto the system and do you have to load an operating system first? Any chance you can post a copy of the DEC Basic code?
 
Thanks. I think many of you can identify with the thrill of seeing this finally work after all this effort.

You toggle in the bootstrap loader to tell the system how to read in the absolute loader
You run the bootstrap to read in the absolute loader
You run the absolute loader to load the BASIC tape (takes 20-30 minutes to load BASIC from tape)
BASIC starts automatically

Once in core, you can switch off the machine and BASIC will still be at 000 000, i.e. you don't have to re-load the tape as long as BASIC is preserved in core.

I bet the PDP 11 BASIC is online someplace already, if it's not I will archive the tape and post on my site.
 
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This is a terrific achievement, thank you for the video (and your other videos too). I'm hoping to be at a stage similar to this someday and I really appreciate you and others here sharing your knowledge. I'm a complete newbie with the 11/05 and can't contribute anything, wish I could. But knowing that there is a massive collected experience here at hand is a great relief.
Please keep up the impressive and informative 'adventures in PDP-11 land' postings and vids!

Steve.
 
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