I use some pins in P3 as input pin and other pins in P3 as output pin. Use C program to read or write the pin directly, e.g. P35 = 0; if(P32 == 0) etc. But if I read a pin, all pins in P3 will become to 1. I debug the program in simulation not in physical MCU.
Are you sure this is a problem, i.e. have you read up on the specific behaviour of the ports, where the port pins can be driven low with strength, but can only be held high with a weak pull-up?
So to use them as inputs, you write a one to the port to make use of the weak pull-up and have an external signal override.
Another thing - you say you simulate. Have you written any scripts to stimulate the processor pins, or exactly what are your virtual processor expected to see on the processor pins?