In a lesson I want to explain asynch serial data format and RS232 signal 
levels.

AFAIK the RS232 signal levels predate the 5V TTL levels (correct)?

The TTL-RS232 level converters/shifters are all inverting. Does anyone 
know why? Because inverting drivers are slightly easier to build? Or 
were the asynch-on-TTL levels chosen first, and as a consequence the 
drivers had to be inverters?

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Wouter van Ooijen

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

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