Bin to hex converter in 16-bit DOS assembly

Just a quick code like putting your keyboard where your brain is. There should be another way of doing this. I hate this code.

start:
        xor al, al
        xor bl, bl
        xor cl, cl
        mov dl, 4       ; use dl as counter
	
input:
        mov ah, 00
        int 16h
        cmp ah, 1ch
        je exit
        cmp al, '0'
        jb input
        cmp al, '1'
        ja input
	
convert:
        mov cl, dl
        dec cl          ; dl - 1
        sub al, 30h     ; get original value
        shl al, cl      ; place in the appropriate bit position
        or bl, al       ; save in bl
        dec dl          ; prepare for the next bit
        jnz input       ; must be 4 bits
        cmp bl, 9
        ja letter
        jbe number
	
letter:
        add bl, 37h     ; because 'A' - 37h is 0Ah
        jmp here
	
number:
        add bl, 30h     ; because '0' - 30h is 00h
	
here:
        call display
        jmp start
	
display:
        mov ah, 02h
        mov dl, bl
        int 21h
ret
	
exit:
        int 20h

Try this out, get the assembler here.