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pdp 11/05 - back to vintage stuff

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  • B Degnan
    Since VCF E I have been working to finish up on my PDP 11/05 project. I put together another teletype that will be dedicated to the PDP 11. Here is an excerpt
    Message 1 of 1 , Jun 1 10:53 AM
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      Since VCF E I have been working to finish up on my PDP 11/05 project.  I put together another teletype that will be dedicated to the PDP 11. 

      Here is an excerpt from my web site:

      More attempts to run a program on a pdp 11/05 that would cause "HELLO WORLD" to print on a teletype model 33 ASR.
      This time I have a second Teletype Model 33 ASR. it is wired for full duplex and 20mA. LOCAL mode works just fine, and I was quickly able to get to my previous stopping point when testing with the 1st TTY.
      I had not attempted any baud rate adjustments yet. Subtle baud controls are found on one of the processor cards (M7260). I put the M7260 card onto a riser so that I could alter the potentiometers that control the baud rate without having to remove the card each time I wanted to make a change. I verified that the radial switch was set to "5". I next started playing with tiny changes to the vertical, blue potentiometer near the upper left corner. I was able to find where I think 110 baud should be, short of breaking out the oscilloscope. I ran a test I found here...

      http://www.pdp-11.nl/pdp...5/cpu/boards/m7260.html
      ...that prints characters and spaces in a pattern. Something like
      @0 @0@ 0 is bad
      @ @ @ @ @ is good (?)   (I have a bad ribbon, I think it's printing @ chars, but it could be * 's.

      I made numerous small adjustments and each time I re-ran the code that is supposed to print HELLO WORLD. No dice. I do get the correct number of characters each time (11), but I still have not been able to print HELLO WORLD.
      Next:
      [1] Try measuring the baud with an oscilloscope.
      [2] Write a program that echoes what I type on the TTY through the computer and back to the printer. Also understand the code behind the program I found on the web that I think says HELLO WORLD, but I don't know for sure. It could have been written for a slightly different output device.
      [3] I am also not sure if the TTY needs a stop bits/parity adjustment.


      More to follow.

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