[GreenKeys] Selectric I/O [OT]

[AA8K73 GMail]

It was 1975 and our organization was changing from
its IBM 1401 to a DEC PDP-11/70.  The PDP-11/70
was delivered, but the 16 terminals were back-ordered
for three months.  Same with the GE TermiNet printer.
So, the only communication we had with the 11/70
was the console DecWriter.

My mentor, Gary Unruh, was an ex-IBMer and had a
Selectric terminal that IBM wore out.  He wrote
a driver for it, I think he named it "TiltAndTwirl",
and we plugged it into the mux and it worked fine.  We
also dug up a 35 KSR that I converted to the RS-232 mux.
Now we had two development terminals and a printer
so we could write our 3GL multi-user language and
software.  We wore that poor Selectric to the
point that it would drop characters and make
grinding noises.  We soon learned which characters
were missing and could make intelligent guesses
as to what was printed.  It gave the last of its
life for us and served us in a time of need, but
we were sure glad to see the DecScopes arrive.


Oh, we bought a punched paper tape reader from a
surplus house, but it had no interface boards.  I
made an interface to RS-232.  I would give it an
advance command and read the character from my
hardware buffer, then another cycle.  We used it
to read PPT from the field offices that were
using Friden Flexowriters to prepare tapes.
Another data format?  No problem with assembler.

I also made a special clock board that I inserted
into the PDP 11/70 that allowed me to slow down
a UART to 45.45 baud.  Then I wrote a driver that
let me read five-level.  I had my transceiver at
the office and I monitored the 20 meter autostart
frequency all day long, through my kit HAL ST-6,
writing it to a disk file.

Doing it in software sure made auto LF and unshift
on space a simple trick.


Gary and I did an interface to the IBM 1401 (RTL
to TTL).  We grabbed signals right off the 1401
processor (Autocoder) and sent them to a home-brewed
interface board (that we hid under the raised floor)
that latched and fed them to the RS-232 mux.  That
is how we got our large data files from 1401
7 track tape to 11/70 disc files.

So, that PDP-11/70 was talking ASCII, Selectric,
Autocoder, 7 Track, Flexowriter, and Baudot.


Mike - AA8K

CR CR LF Ltrs Ltrs

NNNN



On 12/31/2010 08:05 PM, Keith Densmore wrote:
> Power to the Green in 2011,
>
> I came across an interesting old advertisement on Ebay for   a IBM Selectric
> Terminal. This unit was put together by a company called Data-Trans and was
> a 300 baud printing terminal.
> The ad is here
> 190361445421
>
> Any list members have, use,  or even know of the existence of any of these
> old terminals? I know IBM had several versions of Selectric Teminals over
> the years but most used non standard codes. But it might be possible to do a
> data conversion with some modern electronics.  It would be cool to see one
> running with HeavyMetal. Just trying to dream up more weird projects for the
> new year.
>
> 73,
> Keith ve3ts
>