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

[Paul Wills]

Funny you should bring that up.  My first "printing terminal" for my IMSAI 
was a model 15 teletype.  Prior to that, I used a parallel keyboard and 
converted television set for display.  I knew little about serial data 
transmission and nothing about Baudot.  In fact, had I known anything, I 
probably wouldn't have taken the project onl.  I wrote a set of assembly 
language routines to send and receive to the TTY, built an interface circuit 
and probably learned more from that experience than from most anything else 
I had done.

Both the computer and printer are still working fine.

PDW

----- Original Message ----- 
From: "Clay Archer" <carcher at parkcity.net>
To: "'greenkeys'" <greenkeys at mailman.qth.net>
Sent: Tuesday, March 19, 2013 6:02 PM
Subject: Re: [GreenKeys] Current Loop to RS-232 Conversion on ASR33


>
> 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.
>
>