Verilog Coding Tips and Tricks: Verilog code for BCD to 7-segment display converter

Tuesday, October 27, 2015

Verilog code for BCD to 7-segment display converter

A seven-segment display (SSD) is a form of electronic display device for displaying decimal numbers. They can be used as an alternative to complex display's such as dot matrix.

A SSD has 7 segments and theoretically we can use it to display 2^7 = 128 combinations of characters. But most of these combinations, doesn't make sense to a human eye. Decimal numbers can be displayed correctly on a 7 segment panel as shown below:

 



The image on the right indicates the order in which the panels are accessed normally. This is done using a 7 bit vector.

Here, I have written a Verilog code which takes in a BCD number and converts it into a 6 bit vector format, which the seven segment panel understands. Note that, to light up an individual panel, we have to switch it OFF(pass '0' through it).

Seven segment display Code:

//Verilog module.
module segment7(
     bcd,
     seg
    );
     
     //Declare inputs,outputs and internal variables.
     input [3:0] bcd;
     output [6:0] seg;
     reg [6:0] seg;

//always block for converting bcd digit into 7 segment format
    always @(bcd)
    begin
        case (bcd) //case statement
            0 : seg = 7'b0000001;
            1 : seg = 7'b1001111;
            2 : seg = 7'b0010010;
            3 : seg = 7'b0000110;
            4 : seg = 7'b1001100;
            5 : seg = 7'b0100100;
            6 : seg = 7'b0100000;
            7 : seg = 7'b0001111;
            8 : seg = 7'b0000000;
            9 : seg = 7'b0000100;
            //switch off 7 segment character when the bcd digit is not a decimal number.
            default : seg = 7'b1111111; 
        endcase
    end
    
endmodule

Testbench:

module tb_segment7;

    reg [3:0] bcd;
    wire [6:0] seg;
    integer i;

    // Instantiate the Unit Under Test (UUT)
    segment7 uut (
        .bcd(bcd), 
        .seg(seg)
    );

//Apply inputs
    initial begin
        for(= 0;< 16;= i+1) //run loop for 0 to 15.
        begin
            bcd = i; 
            #10; //wait for 10 ns
        end     
    end
      
endmodule

Simulation Waveform:

The codes were correctly simulated in Xilinx ISE 13.1. Check the waveform below:


2 comments:

  1. Hi, Im having a really odd error where there appears to be a ghost number when 5 or 6 are selected but not with any other number

    ReplyDelete