I have made sample code for 4 bit ALU and 3 to 8 decoder to make 4 bit processor . as designer we can design anything so I have started to design processor with two function ALU and decoder 4 bit alu Module alu (a,b,s0,s1,s2 f); Input a,b,s0,s1,s2; Output f; Reg [3:0]; Always @(s0,s1,s2); Begian Case (s0,s1,s2); 3b’000 :f=(a&b;); 3b’001:f= (a|b); 3b’010 :f= ~(a&b;); 3b’011 :f= ~ (a|b); 3b’100:f=(a^b); 3b’101: f=(a*b); 3b’110: f=(a+b); 3b’111:f=(a-b ); End case End module 3to 8 decoder Module decoder (a2,a1,a0, d7,d6,d5,d4,d3,d2,d1,d0); Input a2,a1,a0; Output d7,d6,d5,d4,d3,d2,d1,d0; Wire [7:0]; Always @(a2,a1,a0); Begin Case (a2,a1,a0); 4’b000:( d7,d6,d5,d4,d3,d2,d1,d0)=00000001; 4’001: (d7,d6,d5,d4,d3,d2,d1,d0)=00000010; 4’b010: (d7,d6,d5,d4,d3,d2,d1,d0)=00000100; 4’b011: (d7,d6,d5,d4,d3,d2,d1,d0)=00001000; 4’b100:( d7,d6,d5,d4,d3,d2,d1,d0)=00010000; 4’b101:( d7,d6,d5,d4,d3,d2,d1,d0)=00100000; 4’b110: (d7,d6,d5,d4,d3,d2,d1,d0)=01000000; 4’b111: (d7,d6,d5,d4,d3,d2,d1,d0)=10000000; Endcase Endmodule I don't understand how to connect 4 bit Alu with 3 to 8 bit decoder to make 4 bit processor