la r1, 127         base address is 127
ld r4, 387(r1)     read parallel port and save in r4
ld r5, 387(r1)     read parallel port and save in r5 
add r2, r4, r5     add r4 and r5, save in r2
st r2, 389(r1)     store in parallel output
la r4, 10          store A in r4
la r5, 11          store B in r5
la r6, 12          store C in r6
la r7, 13          store D in r7
st r4, 393(r1)     display in hex display an A
st r5, 394(r1)     display in hex display an B
st r6, 395(r1)     display in hex display an C
st r7, 396(r1)     display in hex display an D
stop