Elliott 5-level code: just in case you have some oddball 5-level paper tapes
tshoppa at wmata.com
Fri Apr 26 07:49:43 CDT 2019
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.
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