I have been attempting to get my ASR33 teletype connected to something
and communicating, but so far I have not been successful. I have built
the interface here :
http://www.daedalus.co.nz/~don/computing/20mahack.html , but it didn't
seem to work at all. I connected the teletype to a PC clone running
Linux. I set the baud rate to 110 and tested it with a DEC VT100 set to
110 first, to make sure that the PC was communicating over the serial
port properly. Then, I plugged in the teletype in place of the terminal
with the little kludged adapter, crossed my fingers and turned to knob
to the left. The teletype just rattled, not printing anything, and
nothing from the keyboard printed either. Then, I turned the knob to
the right. The teletype works fine, just as it had before. I can type
on the paper, punch tape, etc. Before, when I was just testing the
teletype without connecting it to anything, I got the exact same
results - with the knob to the left, it just rattles, almost like
"Break" is held down. When the knob is turned to the right, it works
like a very heavy, loud, electric typewriter, and I can punch tape. On
my teletype, the knob isn't labeled, but I am assuming that the knob
must be Line/Off/Local. Does anyone have any ideas on how I can get
this to talk to something? I don't know a lot about teletypes, but I
downloaded the wiring diagrams from pdp8.net, and have been trying to
figure it out. I think I am connecting it to the correct terminals on
the barrier strip, based on what the wiring diagrams say, but then
again, I might have something wrong. One problem is that I don't know
what the Teletype is _supposed_ to do. I have never seen one
operational, so I don't know if the constant rattleing if not connected
is normal or not. There might be something wrong with it that I don't
know, but chances are, it's just something I am doing wrong.
I got suggestions to try using an old Apple Serial card, or an original
IBM XT card to connect the teletype to, but I have neither. I have
several Super Serial Card II's, as well as several early clone XT
serial cards, but I don't think that they will work. At this point, I
don't really care what I connect the teletype to, I would just like to
get it to do something, and verify that it works.
Eventually, I would like to build an RS232 adapter that would allow me
to use the teletype on PC clone hardware, Pr1me hardware, whatever. I
understand that the teletype uses a 20mA current loop, but I'm afraid
that I don't really know anything about current loop technology. Anyone
have some schematics for a true 20mA to RS232 adapter? Something tells
me that this little kludge I found on the 'net probably isn't the best
or most reliable way to do this.
Any help would be greatly appreciated. Thanks!
Ian Primus
ian_primus_at_yahoo.com
Received on Fri Oct 03 2003 - 19:24:36 BST