How to do this routine in assembly show 3 digits on the screen?

I have the following code in avr assembly. link

The teacher passed this code and asked us to have the program show a 3-digit result on the lcd screen, since now it only accepts 2. The routine is this:

converte_ascii_2d:  ld temp, -X
                    mov temp2, temp
                    clr temp3

Could you give me a hint how to do this?