alu.txt

算术逻辑运算单元

算术逻辑运算单元，它根据输入的8种不同操作码分别实现相应的加、与、异或、跳转等基本操作运算。利用这几种基本运算可以实现很多种其他运算以及逻辑判断等操作。
module alu (alu_out,zero,data,accum,alu_clk,opcode);
output [7:0]alu_out;
output zero;
input [7:0]data,accum;
input [2:0]opcode;
input alu_clk;
reg [7:0] alu_out;

parameter  HLT =3'b000,
           SKZ =3'b001,
           ADD =3'b010,
           ANDD=3'b011,
           XORR=3'b100,
           LDA =3'b101,
           STO =3'b110,
           JMP =3'b111;

assign zero=!accum;
always@(posedge alu_clk)
   begin
      casex(opcode)
        HLT:alu_out<=accum;
        SKZ:alu_out<=accum;
        ADD:alu_out<=data+accum;
        ANDD:alu_out<=data&accum;
        XORR:alu_out<=data^accum;
        LDA:alu_out<=data;
        STO:alu_out<=accum;
        JMP:alu_out<=accum;
        default:alu_out<=8'bxxxx_xxxx;
      endcase
   end
endmodule