Address extending control unit

摘要

An address extending control circuit is disclosed which is provided with a memory having a memory capacity larger than that assignable with the content of an address register. The memory area of the memory is divided into a common block and a plurality of segment blocks of variable capacity. In a certain processing, the common block and any one of the segment blocks are utilized in pairs, thereby to obtain an extended address. To this end, an address extending address register capable of selecting a predetermined segment block of the memory is provided in addition to the address register. When the value in the address register is detected to be larger than a predetermined value, the content of the address extending address register corresponding thereto is appended to the content of the address register to increase the number of bits and a combination of the common block with one segment block of the memory is selected, with which an address in the selected segment block is accessed. Thus, address extending can be achieved with a simple construction.