Is this the right code? It does not do anything but subtract 2 from 2, and jumpos to Label_2 always.

Basically there is no "sub" instruction in the MCS-51 instruction set, so you have to make sure the carry isnt set, to avoid inadvertant accounting of borrow value. the instruction following subb will jump to Label_1 if carry is set, that means the second number is greater than the first (here both are 2), or if the result is 0 or positive, it will jump to Label_2

MOV A, #2
CLR c
SUBB A, #2
JC, Label_1
SJMP Label_2

btw, no comma is needed after JC.

girish