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

Question

I have the following code in avr Assembly. link

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

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

Could you give me a tip on how to do this?