Research And Implementation Of Model Machine Based On Combinational Logic Controller

Principles of computer composition, involving many aspects such as hardware, software,digital circuits, programming methodology, etc, is one of the core curriculums in computerscience field, Recently, colleges have been paying more and more attention to the experiments ofthe curriculum since they can provide students a hands-on opportunity to simulate simplecomputers, making students further understand the principles of computer organization. Themodel machine, according to the difference of controllers, can be divided into two types whichare based on combinational logic and microprogram control unit respectively. In order to enrichthe teaching and experiments of composition principles, and to comprehend the inner structureand working principles of CPU, this paper designs and realizes a combinational logic modelmachine.The combinational logic model machine is designed in accordance with the Von Neumannstructure, with an eight-bit bus width. Its instruction system, referring to the reduced instructionset computer(RISC), has twenty three function instructions and three panel instructions includingregister operation instructions, memory access instructions, jump instructions and I/Oinstructions, which are simple and frequently used. Its controller, designed following the CPLD,decodes the instructions by the instruction decoder. The machine cycle has eight clock cycles,making sure that most instructions can be finished in one cycle, except that few complicatedinstructions still need two cycles. The formation of control signals is analyzed and their logicexpressions are given, on the basis of which, the combinational logic circuit is fabricated and thedesigned controller, combined with the peripheral ALU and memory, compose a complete modelmachine.The combinational logic control model machine is faster than the model machine controlledby the microprogram. Furthermore, the design of controller, when following the CPLD, is moreflexible, and the size of the machine is reduced, thereby improving the whole performance.