A couple. For starters, take a look at your delay routine:

delay_ms:
        mov     r7, #00h
loop_1:
        inc     r7
        mov     a, r7
        cjne    a, #0ffh, loop_1
        ret

If you can arrange it so you count down instead of up in your loops, the DJNZ instruction can make them somewhat less clumsy, like this:

delay_X:                        ; Delay for unknown time
        mov     r7,#00h         ; Initialize counter
        djnz    r7,$            ; Decrement counter to zero
        ret                     ; Done

Of course this will give a shorter delay than the original. Hence the new name.

The other problem with both of these delay loops is that the delay time will vary depending on the speed of the processor. So if you move your code to a different 8051 variant or even just change the clock speed, your program may no longer work because the delays will all be wrong.

The solution is to use timer interrupts to establish your delay times. Your programs will be a little bit more complicated, but it will be much easier to reuse your code on different processors if you avoid delay loops like the ones above.

-- Russ