"The Carry bit (C) is set if operand1 is less than operand2, otherwise it is cleared."

mov	a,dph
cjne	a,#075h,Next
jnc	error     ;if c is set, acc must be lower than 75h 
                  ;if c is clr, acc is higher or equal to 75
Next:
;if we get here, acc is lower than 75h

Error:

;if we get here, acc is higher than 75h