I could find some codes that make this, but could not really understand what they do, or why they do that way, I would like know some teory behind this, to understand, google dont says much specifically about this, someone can give some help to my neurons?

"Converting" a 16-bit value to ASCII is basically just a change of the base of the number - from base-2 (or base-16) to base-10.

The most important thing to know is that the digits (dn...d0) of a base-10 number represent the value of the number in the following way: value = (10^0)*d0 + (10^1)*d1 + ... + (10^n)*dn. If you know the maximum number of digits that the number will have in base-10 (5 for a 16-bit integer), then it's easy to calculate dn ... d0 iteratively using integer division:

dn = value / (10^n)
value = value - (dn * 10^n)
d(n-1) = value / (10^(n-1))
value = value - (d(n-1) * 10^(n-1))
...
d1 = value / 10^1
value = value - (d1 * 10^1)
d0 = value

 

The nice thing is that this is independent of the base that value uses natively, e.g. it doesn't matter whether the "system" represents numbers in base-2, base-10, base-16 or base-371 (*shudder*). It also works for conversion to other representations than base-10 - just replace the 10 by the desired base (and remember that number of digits may change, too).