Scrolling or Moving Text Using 7 Segment LED's in Verilog | FPGA

This one is going to be a quick easy project. The objective here is to get use the 7-segment LED display on the board to display a scrolling text. it should be slow enough so that it can be easily read.

I have made the delay between each word shift to be 1 second. This is long enough to read the text comfortably without missing anything. I have explained in my previous post how to create an accurate delay using verilog, you can read about it there: Create accurate delay in Verilog. Now since I need a 1 second delay here the counter monitoring this count must count to 50,000,000. And the register needed to hold this count must be 29 bits wide.

Using this method you can scroll and display anything. Here I have chosen to display the text "Hello There" to scroll across the LED's and appear to be continuous without any stops. The concept is pretty simple. I create a separate counter that increments every time a count of 50,000,000 is reached. This counter will count till 8, display the entire text, and then reset back to 0 so that the text can be scrolled again. For every count increment it will match it with a case statement. This case will instruct the display for that second.

Now since 7 segment LED's are being used here you must have a proper understanding of them before trying to read and understand the code. I have detailed the topic in detail here: 7 Segment LED Multiplexing in Verilog. Be sure to read and understand it.

So instead of displaying numbers the plan is to display letters on the LED's. This can be achieved by changing the case statement to our requirements.

As usual the code is commented in detail and should be self explanatory even without the above rant. A video demonstration has been added at the end.

module scrolling_name(
    input clock,
    input reset,
    output a,
    output b,
    output c,
    output d,
    output e,
    output f,
    output g,
    output dp,
    output [3:0] an
    );

reg [28:0] ticker; //to hold a count of 50M
wire click;
reg [3:0] fourth, third, second, first; // registers to hold the LED values

always @ (posedge clock or posedge reset) //always block for the ticker
begin
 if(reset)
  ticker <= 0;
 else if(ticker == 50000000) //reset after 1 second
  ticker <= 0;
 else
  ticker <= ticker + 1;
end

reg [3:0] clickcount; //register to hold the count upto 9. That is why a 4 bit register is used. 3 bit would not have been enough.

assign click = ((ticker == 50000000)?1'b1:1'b0); //click every second

always @ (posedge click or posedge reset)
begin
 if(reset)
  clickcount <= 0;
 else if(clickcount == 8)
   clickcount <= 0;
  else 
  clickcount <= clickcount + 1;

end

always @ (*) //always block that will scroll or move the text. Accomplished with case
begin
    case(clickcount)
    0:
    begin
     fourth = 4; //H
     third = 3; //E
     second = 7; //L
     first = 7; //L
    end
    
    1:
    begin
     fourth = 3; //E
     third = 7; //L
     second = 7; //L
     first = 0; //O
    end
    
    2:
    begin
     fourth = 7; //L
     third = 7; //L
     second = 0; //O
     first = 2; //-
    end
    
    3:
    begin
     fourth = 7; //L
     third = 0; //O
     second = 2; //-
     first = 1; //T
    end
    
    4:
    begin
     fourth = 0; //O
     third = 2; //-
     second = 1; //T
     first = 4; //H
    end
    
    5:
    begin
     fourth = 2; //-
     third = 1; //T
     second = 4; //H
     first = 3; //E
    end
    
    6:
    begin
     fourth = 1; //T
     third = 4; //H
     second = 3; //E
     first = 8; //R
    end
    
    7:
    begin
     fourth = 4; //H
     third = 3; //E
     second = 8; //R
     first = 3; //E
    end
    
    8:
    begin
     fourth = 3; //E
     third = 8; //R
     second = 3; //E
     first = 2; //blank
    end
  endcase
  
end

//see my other post on explanation of LED multiplexing.

localparam N = 18;

reg [N-1:0]count;

always @ (posedge clock or posedge reset)
 begin
  if (reset)
   count <= 0;
  else
   count <= count + 1;
 end

reg [6:0]sseg;
reg [3:0]an_temp;

always @ (*)
 begin
  case(count[N-1:N-2])
   
   2'b00 : 
    begin
     sseg = first;
     an_temp = 4'b1110;
    end
   
   2'b01:
    begin
     sseg = second;
     an_temp = 4'b1101;
    end
   
   2'b10:
    begin
     sseg = third;
     an_temp = 4'b1011;
    end
    
   2'b11:
    begin
     sseg = fourth;
     an_temp = 4'b0111;
    end
  endcase
 end
assign an = an_temp;

reg [6:0] sseg_temp; 
always @ (*)
 begin
  case(sseg)
   4 : sseg_temp = 7'b0001001; //to display H
   3 : sseg_temp = 7'b0000110; //to display E
   7 : sseg_temp = 7'b1000111; //to display L
   0 : sseg_temp = 7'b1000000; //to display O
   1 : sseg_temp = 7'b0000111; //to display T
   8 : sseg_temp = 7'b0001000; //to display R
   
   default : sseg_temp = 7'b1111111; //blank
  endcase
 end
assign {g, f, e, d, c, b, a} = sseg_temp; 
assign dp = 1'b1;

endmodule