Stage Computation: Arith/Log. Ops P283 igure 4.16 OPl A, rB icode:ifun←-M1[Pc] Read instruction byte rA:rB←M1[Pc+们 Read register byte Fetch vaIP tPC+2 Compute next PC vaA←R[A Read operand a Decode vaB←R[rB] Read operand B vale t valB oP valA Perform ALU operation Execute Set cc Set condition code register Memory Write RrB]←vaE Write back result back PC update PC←vaP Update Pc a Formulate instruction execution as sequence of simple steps a Use same general form for all instructions 10-MPC]表示从PC开始的内存中读取一个字节的数据 Processor– 10 – Processor Stage Computation: Arith/Log. Ops P283 Figure 4.16 ◼ Formulate instruction execution as sequence of simple steps ◼ Use same general form for all instructions OPl rA, rB icode:ifun  M1 [PC] rA:rB  M1 [PC+1] valP  PC+2 Fetch Read instruction byte Read register byte Compute next PC valA  R[rA] valB  R[rB] Decode Read operand A Read operand B valE  valB OP valA Set CC Execute Perform ALU operation Set condition code register Memory Write R[rB]  valE back Write back result PC update PC  valP Update PC M1 [PC] 表示从PC开始的内存中读取一个字节的数据