What's a "computer console" selectric called? - test-drb@ccmp.vtda.org

28 May 1999

At 10:37 AM 5/28/99 -0500, you wrote:
...
 	<snip>

I don't think the Model 735 Selectric could even handle EBCDIC directly.  I
seem to recall the electrical interface was defined as tilt-and-rotate
signal names.   My Selectric terminal certainly didn't do any translation by
itself from character-codes to solenoid signals, at least not from ASCII.  I
had to do translation myself before sending to the printer.  One way would
have been with hardware between the computer and the Selectric, eg- using an
eprom to translate each ASCII code into the correct combination of Selectric
tilt-and-rotate signals.  My lazier way was to simply put a look-up table in
my driver code, to intercept each ASCII character enroute to the printer and
translate it into the appropriate pattern of solenoid signals first.
Imagine if you had to drive a dot-matrix print head with raw pin-driver
signals instead of the printer hardware figuring it out for you :  same kind
of problem. 
In the CDC-3300 and 3500, most of the "logic" in the operator console, as I
remember from the prints, was related to driving the console typewriter.
The "API" for the typewriter was a  BCD (6 bit) similar to the
"native" code,
but included (in an enhanced mode of operation selected by a console button)
shift codes for selecting lower case/upper case and some extra type-ball
codes.  Normally the printer ran in UPPER CASE only with a few BCD codes
stolen for carriage return, tab and backspace.  No other functions
were available in the normal mode of operation.

I'd guess the logic for this took about 50 or so circuit modules (little
3x3 inch cards with a few transistors each - probably the equivalent to
a single TTL IC in functionality.  I don't recall if there was a diode
rom, though.

As for ASCII, the 3300 didn't know nothing about ASCII.  However, if you
had the BDP (Business Data Processor) as an option, you could do ASCII
string operations (including some arithmetic, if I recall.)  e.g.
"strcpy" and "strcmp" were single instructions (after some setup
code.)
But the BDP was a dog and crashed a lot.  It was only used by the Cobol
compiler.

...

Some vendors did indeed supply an interface that took ASCII from the
computer and sent the necessary tilt-and-rotate signals out to the
Selectric.

Arlen
--
Arlen Michaels     amichael(a)nortelnetworks.com
Nortel Networks, Ottawa, Canada 

Gary