[GreenKeys] UGC-136

[Harold Hallikainen]

On Fri, July 18, 2025 9:10 am, Nick England wrote:

> Huh - I found this in a 1986 DCA report on UHF SATCOM -
> "A prevailing problem is the teletype ASCII character length where the
> Navy
> uses 7-bit and the Air Force uses 8-bit"
>

What to do with the eighth bit has been interesting. ASCII is only 7 bits,
so you don't need to transmit an 8th bit. But computers are based on
bytes. So, the 8th bit was often transmitted as:

Always 0 (space)
Always 1 (mark), same as two stop bits
Even Parity
Odd Parity
Extend the character set (IBM graphic characters)

The parity bit gave very crude error detection, but not correction. If a
character was in error, there was a 50% chance that the parity would not
catch the error.

I think the most clever use of the bit is UTF-8 which allows encoding code
points up to U+10FFFF. I wrote a UTF-8 decoder that handled code points to
U+FFFF and converted everything to a 16 bit characters that then indexed
into an SPI flash memory chip to get the Unifont bitmap of the glyph for
display. This was used in several products, one of which is still in
production.

Anyway, I think UTF-8 is VERY CLEVER!

Harold
https://w6iwi.org


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