I was having similar problems when I made my first test circuit. I believe you problem is where you initialize the SP. I'm still very new as well and would like to know if this is correct.

I made a little program that responds to any pin on P1 going high. The corresponding pin on port 3 will light up the LED. I
try initializing in this order:


$MOD52
org 0h
mov sp,030h ;init stack pointer
org 0100h
mov P1,000h ;clear P1 "inputs"
LOOP:
mov r0,P1
mov P3,r0
jmp LOOP;
end

All LEDs shoulod be off when you reset or start up. Just take a jumper from Vcc and hit any pin on P1 the LED on P3 should light up!

Good luck!
Brian