Data communications system with address remapping for expanded external

Abstract

A data communications system memory interface circuit (32) is provided which operates within an adapter circuit (10). Adapter circuit (10) comprises a communications processor (28), a system interface (30) and a protocol handler (20) coupled together by an adapter bus (26). Communications processor (28) accesses an external memory (38) through a memory interface (32). Memory interface (32) comprises a map register circuit (36) which comprises a number of map registers (44 through 56). The map registers (44 through 56) each are operable to store a portion of a twenty bit address which may be selected by a multiplexer (42) responsive to control signals generated by a control logic circuit (40). The address portion stored in the map registers (44 through 56) are added to a remaining portion of an address to form a complete twenty bit remapped address. In this manner, communications processor (28), using a sixteen bit internal address bus, can access a twenty bit addressable memory space within external memory (38). System interface (30) comprises an address register circuit (34) which allows for the accessing of arbitrary twenty bit addresses or the accessing of addresses using page address numbers and offset values. The protocol handler (20) comprises a page address register (24) which allows for the accessing of external memory (38) on one kilobyte page boundaries.