
19-14
x86 MICROPROCESSORS
The maximum size of ROM is 64K, and so addresses of ROM locations can be
16 bits long. In indexed addressing mode, the DPTR is used as a base address, and the
accumulator is used as an offset. The effective address formed by adding the value of
the base address to the offset, is the ROM address to be accessed. There is the MOVC
instruction especially tailor-made for ROM access.
MOVC A, @A+DPTR is the instruction which loads the content of ROM with
effective address A+DPTR into the A register.
Consider that the ROM location 0500H is to be accessed. The instructions needed
for getting data from the address are as follo ...