1. A hierarchically-structured programmable logic array, comprising: a plurality of sectors, each sector comprising: a plurality of logic cells; and a sector bus system for interconnecting said logic cells within said sector; a block bus system disposed externally to said sectors; and an interface for selectively coupling the plurality of sector bus systems to said block bus system, said interface having a K number of lower level ports coupled to said sector bus systems, and an N number of higher level ports coupled to said block bus system, where N is less than K.