A trace chip monitors a signal between a target logic chip having a data
processing circuit mounted thereon and a memory chip having a memory
storing data to be used by the target logic chip mounted therein, and
traces an operation of the target logic chip. As the trace chip is
implemented by a chip separate from the target logic chip and a memory
chip, a debugging circuit need not be added to mass-produced articles
when the trace chip is not mounted to the mass-produced articles. Thus,
manufacturing cost of the articles can be reduced.