I have some numbers in AH, AL, BL, BH registers. I need to check whether there is 0 bit in each of the registers in left half of the number. If yes, then put into check variable value 10 else -10. How can I do this?

I tried something like that:

org 100h

check dw 0
mov ah, 11111111b
mov al, 11111111b
mov bl, 11111111b
mov bh, 11111111b 
mov check, -10

shr ah, 4
shr al, 4
shr bl, 4
shr bh, 4

cmp ah, 0Fh     

jz first       

first:  

cmp al, 0Fh   

jz second

second:   

cmp bl, 0Fh 

jz third

third: 

cmp bh, 0Fh

jz final  

final:  

mov check, 10    

ret