Instruction address producing unit capable of accessing an instruction segment of an extended size.

摘要

The instruction address producing unit produces an instruction address in response to an entry descriptor (18) in cooperation with a segment descriptor segment (48). The entry descriptor has first and second segment fields (41 and 42) corresponding to first and second instruction descriptors respectively stored in the segment descriptor segment (48) of the memory (10). The first and the second instruction descriptors (51 and 56) are partially read out of the segment descriptor segment (48) to be kept in an instriction segment register (52) and an instruction counter (57), respectively, and to be produced as first and second retained instruction descriptors. An adder circuit (58) adds the first retained instruction descriptor to the second retained instruction descriptor to produce a result of addition as the instruction address to an instruction segment (59) in the memory (10). Each of the first and the second instruction descriptors may be an extended segment descriptor.