simple 8086 compare instruction problem

Question

recently i have a 8086 assembly homework to finish, i try to use the CMP instruction , but can't get it right.here is the code:

MOV AL, 88h
   CMP AL, 24h
   JL  exit
label:
   mov al,4h
exit:
   RET

when i debug it , after jl it jump right to exit: but the following code works fine

MOV AL, 88
   CMP AL, 24
   JL  exit
label:
   mov al,4h
exit:
   RET

why this is happening ?

Answer 1

JL uses a signed condition. From a signed viewpoint, 88h is a negative number. If you want 24h to be treated as less than 88h, you have a couple of choices -- the most obvious would be to use an unsigned condition, which would mean using jb instead of jl.