> But the standard that defines what we call RS232 really came before
> all but the very first primitive commercial ICs (first revision was complete
> ca. 1962), so I think you'll have to look back much further in time to
> see why 1 is defined as < 0 and 0 is defined as > 0.

I agree. But my question was why the TTL 'version' of RS232 (the 
interface between a UART and the driver) is inverted wrt. the RS232, 
which requires the driver (besides shifting the level) to invert. Was 
the inverting driver first and did the UARTs follow, or was it the other 
way round?

> Probably not much different in principle from the ASR33 and TWX/Telex
> machines that some of us old f*rts can remember using.

I had an ASR33 as my first printer on my Exidy Sorcerer (Z80). Lovely 
machine (the ASR33), I still have a bunch of paper tape rolls somewhere.

-- 

Wouter van Ooijen

-- -------------------------------------------
Van Ooijen Technische Informatica: www.voti.nl
consultancy, development, PICmicro products
docent Hogeschool van Utrecht: www.voti.nl/hvu

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