Memory system compatible with a conventional expanded memory

Claim 2

An information processing apparatus defining a window in a portion of an address space of a CPU and accessing a memory area, comprising: a memory section including a plurality of memory blocks, each of the plurality of memory blocks having a set number, each of the memory blocks including a plurality of memory areas, each of the plurality of memory areas having a page number; a page control means, connected to the CPU, for storing mapping information which is supplied from the CPU and which represents a page number of a memory area in which data is stored; a mapping register, connected to the CPU and the page control means, for storing mapping information including set information indicating a set number of a memory block in which the data supplied from the CPU is stored; and a memory control means, connected to the CPU, the page control means, the mapping register and the memory section, for accessing the memory section in accordance with the mapping information stored in the mapping register and the page control means.

Claim 3

An information processing apparatus according to claim 1, wherein the memory control means includes: a read/write controlling circuit, connected to the CPU, the page control means, and the mapping register, for controlling read/write access to the page control means and write access to the mapping register in accordance with a control signal supplied from the CPU; a decoding circuit, connected to the CPU, for detecting a page frame address indicating an address of the window from a memory address supplied from the CPU, and for calculating a position of the window in the address space; an address composite circuit, connected to the CPU and the mapping register, for synthesizing a memory access address from the mapping register using the mapping information supplied through the mapping register, and a system address supplied from the CPU; and a memory controlling circuit, connected to the CPU, the address composite circuit, the mapping register, the decoding circuit and the memory section, for accessing the memory section in accordance with a memory access enable signal generated by and supplied from the mapping register, a page frame decode signal generated by and supplied from the decoding circuit, the memory access address supplied from the address composite circuit, and a memory read/write signal supplied from the CPU.

Claim 4

An information processing apparatus according to claim 1, wherein the memory control means includes: a read/write controlling circuit, connected to the CPU, the page control means, and the mapping register, for controlling read/write access to the page control means and write access to the mapping register in accordance with a control signal supplied from the CPU; a decoding circuit, connected to the CPU, for detecting a page frame address indicating an address of the window from a memory address supplied from the CPU, and for calculating a position of the window in the address space; an address detecting circuit, connected to the CPU, for detecting addresses of a conventional memory which can be directly recognized and accessed by the CPU and an extended memory which can be directly recognized and accessed by the CPU from an address supplied from the CPU; a selected circuit, connected to the CPU and the address detecting circuit, for selecting one of the mapping information supplied through the mapping register and the address supplied from the CPU in accordance with a detecting signal generated by and supplied from the address detecting circuit; an address composite circuit, connected to the CPU and the mapping register, for synthesizing a memory access address from the mapping register using the mapping information supplied through the mapping register, and a system address supplied from the CPU; a calculating circuit, connected to the address detecting circuit and the mapping register, for generating a memory access enable signal in accordance with the detecting signal supplied from the address detecting circuit and the mapping information supplied from the mapping register; and a memory controlling circuit, connected to the CPU, the address composite circuit, the calculating circuit and the memory section, for accessing the memory section in accordance with a memory access enable signal supplied from the calculating circuit, the memory access address supplied from the address composite circuit, and a memory read/write signal supplied from the CPU.