[GreenKeys] Coded Character Sets, History and Development

[Paul Birkel]

Forwarded from Tim Shoppa.  The Mackenzie reference ("Coded Character Sets,
History and Development") can be retrieved from:

https://textfiles.meulie.net/bitsaved/Books/Mackenzie_CodedCharSets.pdf 

-----Original Message-----
Sent: Friday, April 26, 2019 8:50 AM
Subject: Elliott 5-level code: just in case you have some oddball 5-level
paper tapes

Immensely happy this morning to have finally tracked this down. This is a
5-level code by Elliott used on many of their computers.

It seems to have used standard looking 5-level teletype I/O devices but with
custom typewheel and keyboard/function bar encoding.

It has 3 things in common with other 5-level codes:
1: Letter shift and Number/Figure shift
2: Null is all zeroes
3: Letter shift is all ones and also works as delete just like the other
codes

But some interesting properties, different than other 5 level codes:

1: Letter shift has the letters in alphabetic A-Z sequence.
2: In number shift, the lower 4 bits are the digit 0-9, and the upper bit is
a parity
3: Figure shift, space, carriage return, and line feed are at the extreme
top end of the code space right under letter shift.

The code is documented in Figure B.2 of this wonderful document:
http://rabbit.eng.miami.edu/oldcomputers/Elliott-400-series.pdf

I'm a little surprised that my standard character code references don't
mention this. This is a super elegant layout that any of the 1960's
character code standard guys must've known about, but somehow it never made
it into any of my usual reference books.

Maybe MacKenzie was just too dismissive of all 5-bit codes. He mentions ITA2
for a couple pages and then never talks about 5-level codes again, but he
never stops talking about BCDIC and he goes on and on about hypothetical
12-row punchcard ASCII.

Tim N3QE