JPS6482130A - Data processor - Google Patents

Abstract

PURPOSE:To shorten a time required for execution of a machine word instruction by adding an address register into a CPU to hold the sum of the contents of a base register and a constant contained in the machine word instruction and extracting the corresponding value out of the address register as soon as the execution is started for the machine word instruction. CONSTITUTION:A CPU includes a base register serving as an address generating register (constant value B) and an instruction register stores a machine word instruction. This instruction includes a constant used for calculation of the address of a memory. While the sum of the value B of the base register and said constant is calculated by an adder and held by the address registers more than double as much as the maximum value that can be obtained by the absolute value of the constant. When the machine word instruction which produces a memory access is carried out, the value corresponding to the constant value in the machine word instruction is taken out of those values held by the address register and used as an address. Thus it is possible to shorten the time required for execution of a machine word instruction.