ROM_CHECKSUM:
MOV R1, #00H
MOV R2, #00H

MOV DPTR, #00H
rom_loop:

CLR A
MOVC A, @A+DPTR
MOV R1, A
MOV A, R2
ADD A, R1

MOV R2,A
INC DPL
MOV A, DPL
CJNE A, #00H, ROM_LOOP
INC DPH
MOV A, DPH
CJNE A, #00H, ROM_LOOP

RET