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Verilog code for Decoder

Decoder is one of the main combinational components in digital circuits. Decoders are mainly used in memory address decoding and data demultiplexing. 

In this Verilog project, Verilog code for decoder is presented. The decoder is used for memory address decoding.

verilog code for decoder


The decoder as shown in the figure above decodes the 5-bit address input and outputs a 32-bit signal to select the address being written in the memory. To design the decoder, 32 5-input AND gates are used. 

Verilog code for 5 to 32 Decoder:

// fpga4student.com: FPGA projects, Verilog projects, VHDL projects 
// Verilog code for decoder 
// 5-input AND gate 
module AND_5_input(g,a,b,c,d,e);
  output g;
  input a,b,c,d,e;
  and #(50) and1(f1,a,b,c,d),
            and2(g,f1,e);
endmodule
// fpga4student.com: FPGA projects, Verilog projects, VHDL projects 
// Verilog code for decoder 
// Decoder top level Verilog code using 5-input AND gates 
module dec5to32(Out,Adr);
input [4:0] Adr; // Adr=Address of register
output [31:0] Out;
not #(50) Inv4(Nota, Adr[4]);
not #(50) Inv3(Notb, Adr[3]);
not #(50) Inv2(Notc, Adr[2]);
not #(50) Inv1(Notd, Adr[1]);
not #(50) Inv0(Note, Adr[0]);

AND_5_input a0(Out[0],  Nota,Notb,Notc,Notd,Note); // 00000
AND_5_input a1(Out[1],  Nota,Notb,Notc,Notd,Adr[0]); // 00001
AND_5_input a2(Out[2],  Nota,Notb,Notc,Adr[1],Note); //00010
AND_5_input a3(Out[3],  Nota,Notb,Notc,Adr[1],Adr[0]);
AND_5_input a4(Out[4],  Nota,Notb,Adr[2],Notd,Note);
AND_5_input a5(Out[5],  Nota,Notb,Adr[2],Notd,Adr[0]);
AND_5_input a6(Out[6],  Nota,Notb,Adr[2],Adr[1],Note);
AND_5_input a7(Out[7],  Nota,Notb,Adr[2],Adr[1],Adr[0]);
AND_5_input a8(Out[8],    Nota,Adr[3],Notc,Notd,Note);
AND_5_input a9(Out[9],    Nota,Adr[3],Notc,Notd,Adr[0]);
AND_5_input a10(Out[10],  Nota,Adr[3],Notc,Adr[1],Note);
AND_5_input a11(Out[11],  Nota,Adr[3],Notc,Adr[1],Adr[0]);
AND_5_input a12(Out[12],  Nota,Adr[3],Adr[2],Notd,Note);
AND_5_input a13(Out[13],  Nota,Adr[3],Adr[2],Notd,Adr[0]);
AND_5_input a14(Out[14],  Nota,Adr[3],Adr[2],Adr[1],Note);
AND_5_input a15(Out[15],  Nota,Adr[3],Adr[2],Adr[1],Adr[0]);
AND_5_input a16(Out[16],  Adr[4],Notb,Notc,Notd,Note);
AND_5_input a17(Out[17],  Adr[4],Notb,Notc,Notd,Adr[0]);
AND_5_input a18(Out[18],  Adr[4],Notb,Notc,Adr[1],Note);
AND_5_input a19(Out[19],  Adr[4],Notb,Notc,Adr[1],Adr[0]);
AND_5_input a20(Out[20],  Adr[4],Notb,Adr[2],Notd,Note);
AND_5_input a21(Out[21],  Adr[4],Notb,Adr[2],Notd,Adr[0]);
AND_5_input a22(Out[22],  Adr[4],Notb,Adr[2],Adr[1],Note);
AND_5_input a23(Out[23],  Adr[4],Notb,Adr[2],Adr[1],Adr[0]);
AND_5_input a24(Out[24],  Adr[4],Adr[3],Notc,Notd,Note);
AND_5_input a25(Out[25],  Adr[4],Adr[3],Notc,Notd,Adr[0]);
AND_5_input a26(Out[26],  Adr[4],Adr[3],Notc,Adr[1],Note);
AND_5_input a27(Out[27],  Adr[4],Adr[3],Notc,Adr[1],Adr[0]);
AND_5_input a28(Out[28],  Adr[4],Adr[3],Adr[2],Notd,Note);
AND_5_input a29(Out[29],  Adr[4],Adr[3],Adr[2],Notd,Adr[0]);
AND_5_input a30(Out[30],  Adr[4],Adr[3],Adr[2],Adr[1],Note);
AND_5_input a31(Out[31],  Adr[4],Adr[3],Adr[2],Adr[1],Adr[0]); // 11111
endmodule

The decoder is implemented and successfully verified in the Verilog project of 32-bit MIPS processor here. The decoder is used in the register file for address decoding.

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