>I agree. But my question was why the TTL 'version'
>of RS232 (the interface between a UART and the
>driver) is inverted

I suspect the 'logic high = 0' is related to open collector busses being 
commonly used in early TTL before the tri-state devices made their mark on 
the world. This would allow multiple methods of driving the output from a 
UART block made from low integration TTL chips, such as using a seperate 
output buffer to set a 'break' condition.

The resultant signal polarity would then have required inverting buffers to 
drive the standard TTY type interface devices commonly used for I/O, so the 
1488/1489 chips became very common. 

-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist