The microprocessor is provided with a program modification function not attended
with unnecessary branch instructions or interrupt processes. The instruction storage
unit includes read-only-memory (ROM) for storing instructions composing a program
to be processed and a modified instruction storage unit for storing modified instructions
for program modification. When the upper bits of an instruction address supplied
from the program counter match with the upper bits of the modifying address, the
address translation unit translates the upper bits of the instruction address into
the upper bits of the substitutive address where the modified instruction is stored
in the modified instruction storage unit.
