RS485 & RS422 are better than RS232 because,
- RS485 uses differential signals whereas RS232 doesn't
- When you use a differential signal such as RS485 there are two wires for each signal i.e. two wires for transmit and two for recieve so called + and - these two wires are closely twisted over one another. Both the wires carries the same signal but opposite in phase.
- At the receiving at these two opposite phase signals are added up and the difference is taken as the result. It the diffence is more than +200mv than it is taken as binary 1. where as if it is less than -200mv than its considered as binary 0.
- Since the wires are closely twisted over one another thus any noise interference affects both the signals simultaneously thus there is an equal but opposite interference on the two signals. At the receiving end when you add the signals and take the difference of the siganls the equal and opposite interference gets cancelled and you get the correct result.
- In this way RS485/RS422 lines are immune to noise. & hence a better means of communication in noisy or longer distance conditions.

Regards,
Prahlad Purohit