What's a "computer console" selectric called?

From: Gary Oliver <go_at_ao.com>
Date: Fri May 28 14:26:12 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_at_nortelnetworks.com
>Nortel Networks, Ottawa, Canada


Gary
Received on Fri May 28 1999 - 14:26:12 BST