[GreenKeys] Current Loop to RS-232 Conversion on ASR33

[Clay Archer]

My first computer "terminal" back in '77 when I build my first IMSAI 8080
computer was an ASR33 I picked up for about $50.   I used it full duplex to
the Imsai and loaded & saved programs on the paper tape.  I had someone give
me two other ASR33's in about 1980, one had a built-in RS232 converter. I
still have the Imsai and a stack of programs on paper tape (Mits 8K basic,
etc..) but gave away the ASR33's when I moved in 1989.   I recently bought
and restored an ASR33 and have hooked it up to my Imsai to show the
youngsters how we did it in the old days.  I still have some work to do, but
it's mostly working.

Rob:  I recall looking at some photos that I think you posted of your ASR33
and I believe it had an extra power supply installed in what is normally
open area behind the mode switch (under the telephone panel).   The problem
you may be having is that you may already have a loop supply already built
into the ASR33, or at least changes have been made to the receive loop that
are conflicting with your converter.


-----Original Message-----
From: greenkeys-bounces at mailman.qth.net
[mailto:greenkeys-bounces at mailman.qth.net] On Behalf Of Jim Haynes
Sent: Monday, March 18, 2013 8:10 PM
To: Christian Gauger-Cosgrove
Cc: greenkeys
Subject: Re: [GreenKeys] Current Loop to RS-232 Conversion on ASR33

On Mon, 18 Mar 2013, Christian Gauger-Cosgrove wrote:

> Wouldn't computer systems have trended to run an attached '33 as a full
> duplex terminal?
> 
Most of them did.  Now I remember the original Dartmouth/G.E. time
sharing system used half duplex - when you were about to type your
password it would type about 8 characters, CR without doing a LF,
type some more characters, and repeat a few times until there was a
thoroughly blacked-out area where you were going to type the password.
Of course when video terminals came along that trick was totally
useless.

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