without relly understandigng the thread (going general instead of "Ben", I respond to : Why P5.7 is not connected to pin2&3 of Max485? followed by "it is"

The 485 bus is UNIDIRECTIONAL, you must switch between transmit and receive. Pins2&3 determine the direction of the -176 or whatever trabsciever you use.

Erik

PS, remember not to switch till 1/2 bit time after the interrupt.