>I don't know what "-ve logic" is.

I have always understood negative (-ve) logic to be the state where 0 volts
= true or logic 1, and positive (+ve) logic to be when the high voltage
(i.e. > 3 volts for ttl levels) = true or logic 1.

Each has their place, especially when using items like NAND gates and NOR
gates. Thinking in 1's and 0's in the correct type of logic can save a lot
of hassles when using discrete gates.

>> 2. For rs232, logical 1 is represented by a -ve logic?

but this sentence is then not grammatically correct, it should say
"represented by -ve logic?"

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