ALU复用：PC+1/EX/beq FIGURE e4.5.6 Action for R-type Action for memory Action for Step name instructions reference Instructions branches Instruction fetch IR <Memory[PC] Add. PC <=PC+4 Instruction decode/register fetch A<=Reg [IR[19:15]] B<=Reg [IR[24:20]] ALUOut <PC immediate Data Execution,address computation, ALUOut <A op B ALUOut <=A+immediate if (A==B) Register# branch/jump completion PC <ALUOut PC Address Instruction Registers ALU Address Register# Memory access or R-type Reg[1R11:7】<= Load:MDR <MemoryfALUOut] Data Instruction completion ALUOut or memory Register memory Store:Memory [ALUOut]<B Data Memory read completion Load:Reg[IR[11:7]]<=MDR Instruction register PC Address Data Instruction Register Memory or data Registers ALU ALUOut Register Memory Data data Register registerALU复用：PC+1/EX/beq FIGURE e4.5.6