I'm trying to make two atmel AT89C2051's communicate with each other serially but the serial ports on either won't be available because one serial port on one chip connects to the computer and the other one on the other chip connects to a radio unit.
So my thought is to connect an output port (like P1.5) on one microcontroller to P3.2 on the second one to act as a clock, and connect an output port (like P1.4) to P3.7 on the second one to act as data.
I use P3.2 as clock input since its supposed to trigger interrupt 0.
My question is will an external pull-up resistor be required even though I'm not using P1.0 or P1.1? and if so, what is the maximum value the resistor should be?