Currently I've created a rather hardcoded way of multiplying a value by 10. While testing said subroutine, I've noticed that if I call the subroutine more than one time, the value that'll be returned is not the one I anticipated if I step over the call, however if I step into the call it works as intended.

For example:

digit1: 5

fiveThousand:
        call   #multiply10
        call   #multiply10
        call   #multiply10
        mov.b  digit1,R10
       


multiply10:
        mov.b digit1,R12
        mov.b digit1,R13
        add   R13,R12  
        add   R13,R12  
        add   R13,R12  
        add   R13,R12  
        add   R13,R12  
        add   R13,R12  
        add   R13,R12  
        add   R13,R12  
        add   R13,R12  
        mov.b R12,digit1
        mov.b #0,R13
        mov.b #0,R12
        ret

Then the value returned to R10 will be 160, not 5,000 as expected.