Thanks for pointing out the error.

The code had not one but three bugs - possibly I must have corrected them on the machine version and not updated the copy on my notebook, which still reads as March-04-2001 as the date of completion. Memory of what exactly happened is vague.

       MIRRHEX:   	MOV DPTR, #INV_HEX-1 ; -1 was missing
			MOV MIRHEX1,#0FFH    ; # was missing
			MOV MIRHEX2,A
	CHKLUP:    	INC DPTR
			INC MIRHEX1
			MOV A, MIRHEX1
                        CLR C                ; this instr. was missing
			SUBB A, MIRHEX2
			JNZ CHKLUP
			MOV A, #0
			MOVC A, @A+DPTR
			RET

And I have checked this above code segment in Keil IDE with boundary conditions of 0x00, 0xff and a few values in between. Worked OK.

Sorry to have posted the erroneous code.

Raghu