Rodrigo,

I gather we're talking about a x86 style cpu here. firstly, you need to formulate an algorithm, then you can write the code. I'm not going to write the code for you since my x86 assembler is a little rusty and you need to learn.

Anyway,

result = 0
loop:
result = result * 10
get one input character
end of characters? exit
is it a number? if not,exit
subtract ascii offset
result = result + number
goto loop

so for an input of "123"

result = 0, result * 10 = 0, result+number = 1
result = 1, result * 10 = 10,result+number = 12
result = 12, result * 10 = 120, result+number = 123

Now, just write some assembler to perform this task. Job done.