US Patent 7917718 Arrangements having security protection

An external bus interface method including: receiving, via an access control unit, an access request conveyed through an external bus, and judging, via an access judging unit connected to the access control unit, whether the access request is to be honored or rejected, wherein upon receiving the access request, the access control unit sends to the access judging unit an access judging check request signal asking whether the requested address falls within one of access-permitted areas registered in the access judging unit, the access judging unit checks whether the requested address falls within one of the access-permitted areas registered in it and returns to the access control unit, an access judging check result signal indicating whether the access request is to be honored or rejected, and if the access judging check result signal indicates that the access request is to be rejected, the access control unit nullifies the access request.