Hi,my friend suggest that you use a multi cable to connect one port to another port of main micro(8 wire,for example PORTB of micro 1 to PORTC of main micro) and use PEEK and POKE instruction. you put one byte on a port and read it from main micro and you should make a time program to read data on time.
but it is not a good method. it's need a lot of wire and the distance can effect on the voltage,current and also we have noise.